ODBC Connectivity
Contents
1. None Server o Port 3306 C Database User oey ee Password ie Database test MA otet Page Timeout Buffer Size 2048 Details gt gt Ce Cancel Help I Exclusive ca Microsoft SQL Server DSN Configuration Oracle ODBC Driver Configuration DataSouceName racie SO Server 2n0s ere 7 Description Oracle test T Use strong encryption for data TNS Service Name ORCL I7 Perform translation for character data tee stem r Mote ere settings when outputting currency numbers dates and I Save long running queries to the log file Application Oracle Workarounds SQLServer Migration D DOCUME 1 ipley LOCALS 1 Temp QUERY Browse Enable ResultSet Enable Query Timeout 7 Read Only Connection I Long query time milliseconds 99900 Enable Closing Cursors Enable Thread Safety I Log ODBC driver statistics to the log file DADOCUME Nip LS 1Ter BatchAutocommit Mode Commit onlyifalstatements succeed x Numeric Settings Use Oracle NLS settings zl Figure 6 Parts of the ODBC driver configuration screens on Windows XP for Microsoft Access MySQL Connector ODBC 5 1 Oracle s ODBC driver and Microsoft SQL Server 31 C Internals The appendix is in part an aide memoire for the maintainer but may interest the curious user RODBC connection objects are an integer with several attributes they are numbered consecutively in the current session For example2. gt channel lt odbcConnect test gt unclass channel 1 1 attr connection string 1 DATABASE ripley DESCRIPTION myodbc DSN test OPTION 0 PORT 3306 SERVER 1ocalhost attr handle_ptr lt pointer 0x233e6c0 gt attr case 1 nochange attr id 1 11371 attr believeNRows 1 TRUE attr colQuote 1 nen attr tabQuote 1 nen attr encoding 1 nn attr rows_at_time 1 100 attr isMySQL 1 FALSE Most of the attributes record the arguments of odbcDriverConnect The connection string attribute is as returned by SQLDriverConnect and list driver specific parameters separated and perhaps terminated by a semi colon The id attribute is a random integer used for integrity checks and in particular to reject connection objects should they be saved and restored in a different session The isMySQL attribute is used both to select the default quote character and the interpretation of qualifier table names The main structure of the connection is kept as a C struct a pointer to which is passed around as the R external pointer handle_ptr This has a finalizer that will close the connection when there is no longer an R object referring to it ncluding for the end of the R session with a warning unless the connection has already been closed by close or odbcClose In addition a C level table keeps the pointers of the first 1000 connections of an R session to ena
3. Query UPDATE USArrests SET Assault WHERE State Binding Assault DataType 4 ColSize 10 Binding State DataType 12 ColSize 255 Parameters At C level this works by calling SQLPrepare to record the insert update query on the statement handle then calling SQLBindParameter to bind a buffer for each column with values to be sent and finally in a loop over rows copying the data into the buffer and calling SQLExecute on the statement handle The same buffer structure is used as when retrieving result sets The differ ence is that the arguments which were ouptuts from SQLBindCol and inputs to SQLBindParameter so we need to use sqlColumns to retrieve the column characteristics of the table and pass these down to the C interface 34
4. 29 aspx There is also a Visual FoxPro driver and an outdated Oracle driver 32 bit Windows drivers for Access 2007 and Excel 2007 are bundled with Office 2007 but can be installed sepa rately via the installer AccessDatabaseEngine exe available from http www microsoft com downloads details aspx FamilyID 7554f536 8c28 4598 9b72 ef94e038c891 amp DisplayLang en The Access Excel 2010 versions at http www microsoft com downloads details aspx familyid CO6B8369 60DD 4B64 A44B 84B371EDE16D amp displaylang en have a 64 bit version however the 64 bit drivers cannot be installed alongside 32 bit versions of Office as far as we know and definitely not for Office 2007 For recent versions of Mac OS X low cost and easy to use drivers are avail able from http www actualtechnologies com products php these cover MySQL PostgreSQL SQLite one driver SQL Server Sybase Ora 23 cle and a read only driver for Access and related formats including Ac cess 2007 and Excel but not Excel 2007 That SQLite driver needs believeNRows FALSE set Mac OS X drivers for the MySQL PostgreSQL and the major commercial databases are available from http uda openlinksw com Specifying ODBC drivers The next step is to specify the ODBC drivers to be used for specific DBMSs On Windows installing the drivers will register them automatically This might happen as part of the installation on other systems but usually does not Both
5. DataManager to manage both ODBC drivers and DSNs See the unixODBC user manual at http www unixodbc org doc UserManual On Fedora these are in the unixODBC kde RPM It has been announced that they will become separate projects after unixODBC 2 2 14 On Unix alikes DSNs can also be specified in files and the graphical tools just manipulate these files The system wide file is usually etc odbc ini and the per user file odbc ini Some examples of the format are shown figure 5 What fields are supported is driver specific and it can be hard to find doc umentation There is no clear distinction between fields that specify the driver and those which specify the DSN so any parts of the driver spec ification which might differ between connections can be used in the DSN Extra care is needed on a 64 bit version of Windows as this GUI shows only 64 bit settings for ODBC including drivers and DSNs If you are running 32 bit R and hence 32 bit ODBC on 64 bit Windows you need the 32 bit version of the GUI at something like c Windows SysWOW64 odbcad32 exe and beware that both 32 and 64 bit versions are called odbcad32 exe 16 Library 0DBC odbc ini on Mac OS X 26 L ODBC Data Source Administrator User DSN System DSN File DSN Drivers Tracing Connection Pooling About User Data Sources Add dBASE Files Microsoft Access dBASE Driver dbf ndx Excel Files Microsoft Excel Driver sls x
6. Rape 8 double 15 BUFFER_LENGTH DECIMAL_DIGITS NUM_PREC_RADIX NULLABLE REMARKS COLUMN_DEF 1 255 NA NA 0 a2 2 8 NA NA 1 lt NA gt 3 4 o 10 1 lt NA gt 4 4 o 10 1 lt NA gt 5 8 NA NA 1 lt NA gt SQL_DATA_TYPE SQL_DATETIME_SUB CHAR_OCTET_LENGTH ORDINAL_POSITION IS_NULLABLE 1 12 NA 255 1 NO 2 8 NA NA 2 YES 3 4 NA NA 3 YES 4 4 NA NA 4 YES 5 8 NA NA 5 YES This gives the DBMS data by name and by number twice once the number used in the DBMS and once that used by SQL they agree here Other things of interest here are the column size which gives the maximum size of the character representation and the two columns about nullable which indicate if the column is allowed to contain missing values SQL NULLs The result of sqlTypeInfo has 19 columns and in the version of MySQL used here 52 types We show a small subset of the more common types gt sqlTypeInfo channel lt gt c 1 3 7 16 TYPE_NAME DATA_TYPE COLUMN_SIZE NULLABLE SQL_DATATYPE bit 7 1 1 7 tinyint 6 3 1 6 bigint 5 19 1 5 text gt i 65535 1 i mediumtext 1 16777215 sf 1 longtext 1 2147483647 1 i char 1 255 1 1 numeric 2 19 1 2 decimal 3 19 1 3 integer 4 10 1 4 smallint 5 5 1 5 double 6 15 1 6 float T 7 1 7 double 8 15 1 8 date 91 10 1 9 time 92 8 1 9 year 5 4 1 5 datetime 93 21 1 9 timestamp 93 14 0 9 varchar 12 255 1 12 Note that there are both duplicate type names and duplicate type numbers Most DBMSs started with the
7. at http www postgresql org docs 7 2 static odbc html from before it was unbundled There are that the author works for Easysoft is conspicuous 22 drivers for Unix alikes and 32 bit Windows 64 bit Windows support is planned for PostgreSQL 9 0 An SQLite ODBC driver for Unix alikes including Mac OS X and 32 and 64 bit Windows is available from http www ch werner de sqliteodbc Oracle provides ODBC drivers as a supplement to its Instant Client for some of its platforms including 32 64 bit Windows and Linux but not cur rently Mac OS X See http www oracle com technology software tech oci instantclient One quirk of the Windows driver is that the Oracle binaries must be in the path so PATH should include e g c Oracle bin For IBM s DB2 search its site for drivers for ODBC and CLI There are some notes about using this under Linux at http www unixodbc org doc db2 html Mimer www mimer com is a cross platform DBMS with integral ODBC support so The Mimer SQL setup process automatically installs an ODBC driver when the Mimer SQL client is installed on any Windows or UNIX platform The HowTos at http developer mimer se howto index tml provide some useful hints Some details of the 32 bit Microsoft ODBC Desktop Database Drivers for Access Excel Paradox dBase and text files on Windows can be found at http msdn microsoft com en us library ms709326 28VS 85
8. dev or some such will be needed In most cases the package s configure script will find the driver manager files and the package will install with no extra settings However if further information is required use with odbc include and with odbc lib or environment variables ODBC_INCLUDE and ODBC_LIBS to set the include and library paths as needed A specific ODBC driver manager can be speci fied by the with odbc manager configure option with likely values odbc or iodbc if this is done for odbc and the program odbc_config is found it is used to set the libpath as a last resort it is often wrong and to add any additional CFLAGS Sources of drivers A fairly comprehensive list of drivers is maintained at http www sqlsummit com ODBCVend htm and one for unixODBC at http www unixodbc org drivers html unixODBC ships with a number of drivers although in most cases the DBMS vendor s driver is preferred these in clude for MySQL PostgreSQL Mimer and flat files MySQL provides drivers under the name Connector ODBC formerly My ODBC in source form and binaries for all common 32 bit and most 64 bit R platforms PostgreSQL has an associated project at http pgfoundry org projects psqlodbc and another project for at http pgfoundry org projects odbcng and http projects commandprompt com public odbcng Documentation for psqlodbc is currently hard to find but there is some in the PostgreSQL 7 2 manual
9. first six entries are returned by a call to SQLDescribeCol DataType is used to select the buffer to use There are separate buffers for double precision single precision 32 bit and 16 bit integer and character byte data When character data buffers are allocated datalen records the length al located per row which is based on the value returned as ColSize The IndPtr value is used to record the actual size of the item in the current row for variable length character and binary types and for all nullable types the special value SQL_NULL_DATA 1 indicates an SQL null value The other main C level operation is to send data to ODBC driver for sqlSave and sqlUpdate These use INSERT INTO and UPDATE queries re spectively and for fast TRUE use parametrized queries So we have the queries split across lines for display gt sqlSave channel USArrests rownames State addPK TRUE verbose TRUE Query CREATE TABLE USArrests State varchar 255 NOT NULL PRIMARY KEY Murder double Assault integer UrbanPop integer Rape double Query INSERT INTO USArrests State Murder Assault UrbanPop Rape VALUES Binding State DataType 12 ColSize 255 Binding Murder DataType 8 ColSize 15 Binding Assault DataType 4 ColSize 10 Binding UrbanPop DataType 4 ColSize 10 Binding Rape DataType 8 ColSize 15 Parameters gt sqlUpdate channel foo USArrests verbose TRUE
10. in the table Rows in a DBMS table are in principle unordered and so cannot be referred to by number the sometimes tricky question is to know what rows are to replaced We can help the process by giving one or more index columns whose values must match for a data frame the row names are often a good choice If no index argument is supplied a suitable set of columns is chosen based on the properties of the table 3 1 Primary keys and indices When a table is created or afterwards it can be given additional informa tion to enable it to be used effectively or efficiently Primary keys are one usually or more columns that provide a reliable way to reference rows in the table values of the primary key must be unique and not NULL SQL parlance for missing Primary keys in one table are also used as foreign keys in another table this ensure that e g values of customer_id only take values which are included in the primary key column of that name in table customers Support of foreign keys is patchy some DBMSs e g MySQL prior to 6 0 accept specifications but ignore them RODBC allows primary keys to be set as part of the sqlSave function when it creates a table otherwise they can be set by sqlQuery in DBMS specific ways usually by ALTER TABLE that allows up to 255 bytes or characters and some have much larger limits Calling sqlTypeInfo will tell you about the data type limits Columns in a table can be declared as
11. 10 0 5 New Mexico 11 4 6 Michigan 12 1 7 Nevada 12 2 8 Florida 15 4 Note that although there are standards for SQL all the major producers of DBMSs have their own dialects so for example on the Oracle and DB2 systems we tested this query had to be given as these are the SQL wildcards used for example in LIKE clauses gt sqlQuery ch paste SELECT State Murder FROM USArrests WHERE Rape gt 30 ORDER BY Murder or even in upper case Describing how to extract data from databases is the forte of the SQL language and doing so efficiently is the aim of many of the DBMSs so this is a very powerful tool To learn SQL it is best to find a tutorial specific to the dialect you will use for example Chapter 3 of the MySQL manual is a tutorial A basic tutorial which covers some common dialects can be found at http www 1tkeydata com sql sql html tutorials on how to perform common tasks in several commonly used DBMSs are available at http sqlzoo net 2 3 Table Names SQL 92 expects both table and column names to be alphanumeric plus un derscore and RODBC does not in general support vendor extensions for example Access allows spaces There are some system specific quoting schemes Access and Excel allow table names to be enclosed in in SQL queries MySQL by default quotes via backticks and most other systems use the ANSI SQL standard of double quotes The odbcConnnect function allows the specificat
12. C 9075 3 1995 SQL CLI standard A somewhat biased overview of ODBC on Unix alikes can be found at http wuw easysoft com developer interfaces odbc linux html 2 Basic Usage Two groups of functions are provided in RODBC The mainly internal odbc commands implement low level access to C level ODBC functions with sim ilar names The sql functions operate at a higher level to read save copy and manipulate data between data frames and SQL tables The two low level functions which are commonly used make or break a connection 2 1 Making a connection ODBC works by setting up a connection or channel from the client here RODBC to the DBMSs as specified in the DSN Such connections are normally used throughout a session but should be closed explicitly at the end of the session however RODBC will clear up after you if you forget with a warning that might not be seen in a GUI environment There can be many simultaneous connections The simplest way to make a connection is library RODBC 3in most cases with prefix SQL replacing odbc ch lt odbcConnect some_dsn and when you are done with it close ch or if you prefer odbcClose ch The connection object ch is how you specify one of potentially many open connections and is the first argument to all other RODBC functions If you forget the details printing it will give some summary information If the DBMS user and password are needed and not stored in the D
13. LECT column list FROM INFORMATION_SCHEMA vtew name WHERE condition See the Mimer SQL Reference Manual chapter on Data Dictionary views for full details two views are TABLES and VIEWS A session can be set to be read only by the SQL command SET SESSION READ ONLY Mimer uses Latin 1 for its default character types but Unicode types NCHAR and NVARCHAR are also available Unsurprisingly given that the company is Swedish different collations are allowed for both Latin 1 and Unicode character types The char and varchar columns have a maximum size of 15000 bytes the clob data type is available for larger character columns The nchar and nvarchar columns have a maximum size of 5000 characters the nclob data type is available for larger Unicode columns There are corresponding binary varbinary and blob binary data types 21 A Installation RODBC is simple to install and binary distributions are available for Mac OS X and Windows from CRAN To install from the sources an ODBC Driver Manager is required Windows normally comes with one it is part of MDAC and can be installed separately if required Mac OS X since 10 2 has shipped with iODBC which is also available for other Unix alikes But for other systems the driver manager of choice is unixODBC part of almost all Linux distributions and with sources downloadable from http www unixODBC org In Linux binary distribu tions it is likely that package unixODBC devel or unixodbc
14. NGTH SCALE 1 RIPLEY USArrests State 0 SYSIBM VARCHAR 255 0 2 RIPLEY USArrests Murder 1 SYSIBM DOUBLE 8 0 3 RIPLEY USArrests Assault 2 SYSIBM INTEGER 4 0 4 RIPLEY USArrests UrbanPop 3 SYSIBM INTEGER 4 0 5 RIPLEY USArrests Rape 4 SYSIBM DOUBLE 8 0 The CHAR type can have size up to 254 bytes the maximum size of the VARCHAR type is 32762 bytes For larger character strings there is the CLOB type up to 2Gb These types can be used to store data in a MBCS including various Unicode encodings There are corresponding BINARY VARBINARY and BLOB data types SQL Server There are several hundred views in schemas INFORMATION SCHEMA and sys which will be listed by sqlTables and also by the stored procedure sp_tables Another way to list tables is SELECT FROM sysobjects WHERE xtype U where the condition restricts to user tables USE database changes the database in use Types char and varchar have a maximum specified size of 8000 bytes It is possible to use varchar max previously known as text for a limit of 2Gb but this may not work well with the ODBC interface The Unicode types nchar and nvarchar have a maximum specified size of 4000 characters again there is nvarchar max formerly ntext There are corresponding binary and varbinary data types with image as an earlier name for varbinary max 20 Mimer There are tens of views in schema INFORMATION_SCHEMA which can be read by SQL SELECT queries of the form SE
15. Non standard SQL names are allowed here too but the driver maps to in column names Annoyingly sqlTables is allowed to select named ranges only by tableType TABLE but not to select only worksheets There are at least two known problems with reading columns that do not have a format set before data entry and so start with format General First the driver uses the first few rows to determined the column type and is over fond of declaring Numeric even when there are non numeric entries The default number of rows consulted is 8 but attempts to change this in the DSN setup are ignored Second if a column is declared as Text numeric entries will be read as SQL nulls and hence R NAs Unfortunately in neither case does reformatting the column help The connection is by default read only It is possible to de select this in the DSN and the convenience wrapper odbcConnectExcel has a readOnly FALSE argument to do so but this does not support deletion including SQL DROP DELETE UPDATE and ALTER statements In particular sqlDrop will 16 remove the data in a worksheet but not the worksheet itself The driver does allow a worksheet to be updated by sqlUpdate and for a new worksheet with a different name from existing worksheets to be created by sqlSave which also creates a named range As far as we know no similar issues affect the Actual Technologies Mac OS X Excel driver however it allows only read only ac
16. O A Figure 4 The dialog box of ODBCconfig on Fedora 10 Linux and the Con figure screen for the SQLite driver 29 test_mysql Description test MySQL Driver MySQL Trace No Server localhost Port 3306 Database test test_mysq15 Description myodbcd Driver MySQL ODBC 5 1 Driver Server gannet Port 3306 Database ripley test_pg Description test PostgreSQL Driver PostgreSQL Trace No TraceFile ServerName localhost UserName ripley Port 5432 Socket Database testdb ReadOnly 0 test_sqlite3 Description test SQLite3 Driver sqlite3 Database tmp mysqlite3 db Figure 5 A personal odbc ini file from a Fedora 10 Linux system using unixODBC file Things that are often set here are if the connection is read only test_pg is not readonly and the character encoding to be used Command line programs isql unixODBC and iodbctest i0DBC can be used to test a DSN that has been created manually in a file The formats are isql v dsn db_username db_password iodbctest Both give a command line SQL interface use quit to terminate 30 MySQL Connector ODBC Data Source Configuration ODBC Microsoft Access Setup M aS Y Data Source Name MS Access Database Connector ODBC Description m Database m Connection Parameters bacia Data Source Name testdbS Description Select Create Repair Compact r System Database
17. ODBC Connectivity by Brian Ripley Department of Statistics University of Oxford ripley stats ox ac uk July 26 2010 Package RODBC implements ODBC database connectivity It was originally written by Michael Lapsley St George s Medical School University of Lon don in the early days of R 1999 but after he disappeared in 2002 it was rescued and since much extended by Brian Ripley Version 1 0 1 was released in January 2003 and RODBC is nowadays a mature and much used platform for interfacing R to database systems 1 ODBC Concepts ODBC aims to provide a common API for access to SQL based database management systems DBMSs such as MySQL PostgreSQL Microsoft Ac cess and SQL Server DB2 Oracle and SQLite It originated on Windows in the early 1990s but ODBC driver managers unixODBC and iODBC are nowadays available on a wide range of platforms and a version of i0DBC ships with recent versions of Mac OS X The connection to the particular DBMS needs an ODBC driver these may come with the DBMS or the ODBC driver manager or be provided separately by the DBMS developers and there are third party developers such as Actual Technologies Easysoft and OpenLink This means that for some DBMSs there are several different ODBC drivers available and they can behave differently Microsoft provides drivers on Windows for non SQL database systems such as DBase and FoxPro and even for flat files and Excel spreadsheets Actual Technologi
18. SN they can be supplied by e g ch lt odbcConnect some_dsn uid user pwd Users of the R GUI under Windowst have another possibility if an incom pletely specified DSN is given the driver specific Data Source dialog box will pop up to allow it to be completed More flexibility is available via function odbcDriverConnect which works with a connection string At its simplest it is DSN dsn UID uid PWD pwd but it can be constructed without a DSN by specifying a driver directly via DRIVER and more in some cases many more driver specific parameters can be given See the documentation for the driver and Appendix A for more details 2 2 Reading from a database where database can be interpreted very widely including for example Excel spreadsheets and directories of flat files The simplest and most common use of RODBC is to extract data from databases held on central database servers Such access is read only and this can be enforced by settings in the DSN or via permission settings also known as privileges on the database To find out what tables are accessible from a connection ch use sqlTables ch Some drivers will return all visible table like objects not just those owned by you In that case you may want to restrict the scope by e g This does not work from Rterm exe sqlTables ch tableType TABLE sqlTables ch schema some_pattern sqlTables ch tableName some_patt
19. UNIQUE primary keys and such columns are usually used as the basis for table indices but other indices sometimes called secondary indices can be declared by a CREATE INDEX SQL command Whether adding primary keys or other indices has any effect on performance depends on the DBMS and the query 4 Data types This can be confusing R has data types including character double integer and various classes including Date and POSIXt ODBC has both C and SQL data types the SQL standards have data types and so do the various DBMSs and they all have different names and different usages of the same names Double and single precision numeric values and 32 and 16 bit integers only are transferred as binary values and all other types as character strings However unless as is TRUE sqlGetResults used by all the higher level functions to return a data frame converts character data to an date date time class or via type convert You can find out the DBMS names for the data types used in the columns of a table by a call to sq1Columns and further information is given on those types in the result of sqlTypeInfo For example in MySQL TABLE_CAT TABLE_SCHEM TABLE_NAME COLUMN_NAME DATA_TYPE TYPE_NAME COLUMN_SIZE 1 ripley lt NA gt USArrests State 12 varchar 255 2 ripley lt NA gt USArrests Murder 8 double 15 3 ripley lt NA gt USArrests Assault 4 integer 10 4 ripley lt NA gt USArrests UrbanPop 4 integer 10 5 ripley lt NA gt USArrests
20. be converted to and from a suitable representation For example in MySQL we could use enum FALSE TRUE but this is actually stored as char 5 11 Note that to represent NA the SQL data type chosen needs to be nullable which BIT often is not Mimer has a nullable data type BOOLEAN but this is not supported by the ODBC client 4 2 SQLite SQLite s concept of data type is anomalous version 3 does recognize types of data in version 2 everything was a character string but it does not have a fixed type for a column in a table although the type specified in the CREATE TABLE statement is a recommended type for the values of that column Every value is categorized as null integer of length 1 2 3 4 6 or 8 bytes double text UTF 8 or UTF 16 or BLOB a sequence of bytes This does not fit well with the ODBC interface which pre determines a type for each column before reading or writing it the SQLite ODBC driver falls back to a SQL_VARCHAR or SQL_LONGVARCHAR type if the column type is not available 4 3 ODBC data types ODBC defines two sets of data types SQL data types and C data types SQL data types indicate the data types of data stored at the data source using standard names C data types indicate the data types used in the compiled code in the application here RODBC when transferring data and are the same for all drivers The ODBC SQL data types are abstractions of the data types discuss
21. ble odbcCloseAl1l1 to close them The struct is currently defined as typedef struct rodbcHandle SQLHDBC hDbc connection handle SQLHSTMT hStmt statement handle SQLLEN nRows number of rows and columns in result set SQLSMALLINT nColumns 32 int channel as stored on the R level object int id ditto int useNRows value of believeNRows entries used to bind data for result sets and updates COLUMNS ColData int nAllocated SQLUINTEGER rowsFetched use to indicate the number of rows fetched SQLUINTEGER rowArraySize use to indicate the number of rows we expect back SQLUINTEGER rowsUsed for when we fetch more than we need SQLMSG amsglist root of linked list of messages SEXP extPtr the external pointer address RODBCHandle pRODBCHandle Most ODBC operations work by sending a query explicitly or implicitly via e g sqlColumns and this creates a result set which is transferred to an R data frame by sqlGetResults nRows and nCols indicate the size of the pending result set with nCols 1 used if there are no pending results ODBC works with various handles There is a SQLHENV handle for the en vironment that RODBC opens when a connection is first opened or DSNs are listed its main use is to request ODBC 3 semantics Then each connec tion has a SQLHDBC handle and each query statement a SQLHSTMT handle Argument literal TRUE of sqlTables and s
22. cess to Excel files and does not support Excel 2007 2008 x1sx files 8 DBMS specific tidbits This section covers some useful DBMS specific SQL commands and other useful details Recent versions of several DBMSs have a schema INFORMATION_SCHEMA that holds many predefined system views These include MySQL the name of a database mainly populated beginning with MySQL 5 1 SQL Server and Mimer MySQL We have already mentioned USE database as the way to change the database in use SHOW DATABASES lists the databases for which you have some kind of privilege and can have a LIKE clause to restrict the result to some pattern of database names The DESCRIBE table command is a compact way to get a description of a table or view similar to the most useful parts of the result of a call to sqlColumns It is also known as SHOW COLUMNS FROM table SHOW TABLES is the command to produce a table of the tables views on the current database similar to sqlTables For example gt sqlQuery channel USE ripley 1 No Data gt sqlQuery channel SHOW TABLES Tables_in_ripley 1 USArrests gt sqlQuery channel DESCRIBE USArrests Field Type Null Key Default Extra 1 State varchar 255 NO PRI NA NA 2 Murder double YES NA NA 3 Assault int 11 YES NA NA 4 UrbanPop int 11 YES NA NA 5 Rape double YES NA NA 17 SHOW FULL TABLES gives an additional additional column Table_type the types of the tables views There is useful i
23. current ODBC drivers See the help page for sqlTables for some further details For other uses the trick is to select the schema s you want to use which is done via an SQL statement sent by sqlQuery For Oracle you can set the default schema owner by ALTER SESSION SET CURRENT_SCHEMA schema whereas for PostgreSQL the search path can be changed via SET search_path TO schemal schemaz2 In DB2 creating an alias in the current schema can be used to access tables in other schemas and a CURRENT SCHEMA query can be used to change the current schema In MySQL and SQL Server a database can be selected by a USE database query 6 Internationalization Issues Internationalization issues are made more complex by ODBC being a client server system and the ODBC client RODBC and the server may be running on different machines with different OSes on different continents So the client may need some help In most cases numeric data are transferred to and from R in binary form so the representation of the decimal point is not an issue But in some cases it could be e g decimal rather than binary SQL data types will be transferred as character strings and then the decimal point to be used will be taken from options dec if unset this is set when RODBC is loaded from the setting of the current locale on the machine running R via Sys localeconv Some Scurrerntly this is stymied by bugs in the ODBC driver so SQLColumns is unable to repor
24. dditional types for long sequences there are separate ODBC types for SQL_BINARY SQL_VARBINARY and SQL_LONGVARBINARY Binary types can currently only be read as such and they are returned as column of class ODBC_binary which is a list of raw vectors It is possible but rare for the DBMS to support data types that the ODBC driver cannot handle Most DBMSs have binary data types which have no corresponding R data type raw corresponds to a single byte not a fixed or variable length set of bytes these are not currently covered by RODBC 4 1 Data types when saving a data frame When sqlSave creates a table there is some choice as to the SQL data types used The default is to select the SQL data type from the R type via the typeInfo argument to sqlSave If this is not supplied usual a default mapping is looked up using getSqlTypeInfo or by interrogating sqlTypeInfo This will almost always produce the correct mapping for numeric integer and character columns of up to 254 characters or bytes In other cases include dates and date times the desired SQL type can be specified for each column via the argument varTypes a named character vector with names corresponding to some of the names in the data frame to be saved Only a very few DBMSs have a logical data type and the default mapping is to store R logical vectors as varchar 5 For others DBMSs BIT TINYINT or an enumeration type could be used but the column may be need to
25. ed above with names like SQL_INTEGER They include SQL_LONGVARCHAR for large character types and SQL_WVARCHAR for Unicode character types It is usually these types that are returned by number in the SQL_DATA_TYPE column of the result of sqlColumns and SQL_DATATYPE column of the result of sqlTypeInfo The mapping from names to numbers is given in table 1 The only ODBC C data types currently used by RODBC are SQL_C_DOUBLE SQL_C_SLONG 32 bit signed integers and SQL_C_CHAR for reading and writ ing and SQL_C_FLOAT single precision SQL_C_SSHORT 16 bit signed inte gers and SQL_C_BINARY for reading from the database http msdn microsoft com en us library ms713607 28VS 85 29 aspx is the defintiive source of information about ODBC data types 12 SQL_CHAR 1 SQL LONGVARCHAR 1 SQL_NUMERIC 2 SQL_BINARY 2 SQL_DECIMAL 3 SQL_VARBINARY 3 SQL_INTEGER 4 SQL_LONGVARBINARY 4 SQL_SMALLINT 5 SQL BIGINT 5 SQL FLOAT 6 SQL TINYINT 6 SQL REAL 7 SQL_BIT 7 SQL_DOUBLE 8 SQL_WCHAR 8 SQL_DATETIME 9 SQL_WVARCHAR 9 SQL_INTERVAL 10 SQL_WLONGVARCHAR 10 SQL_TIMESTAMP 11 SQL GUID 11 SQL VARCHAR 12 SQL_TYPE_DATE 91 SQL_TYPE_TIME 92 SQL_TYPE TIMESTAMP 93 Table 1 Mapping between ODBC SQL data type names and numbers GUIDs are 16 byte numbers Microsoft s implementation of UUIDs 5 Schemas and Catalogs This is a more technical section few users will need to deal with these concepts Schemas are collections of objects suc
26. er file from a x86_64 Fedora 10 Linux system using unixODBC 25 B Specifying DSNs The ODBC driver managers have User DSNs and System DSNs these differ only in where the information is stored the first on a per user basis and the second for all users of the system Windows has a GUI to set up DSNs called something like Data Sources ODBC under Administrative Tools in the Control Panel You can add remove and edit configure DSNs there see figure 2 When adding a DSN first select the ODBC driver and then complete the driver specific dialog box There will usually be an option to test the DSN and it is wise to do so If Rgui is to be used on Windows incomplete DSNs can be created and the dialog box will be brought up for completion when odbcConnect is called this can be helpful to avoid storing passwords in the Windows Reg istry or to allow alternate users or databases On that platform calling odbcDriverConnect with no arguments will bring up the main ODBC Data Sources dialog box to allow a DSN to be constructed on the fly Mac OS X comes with a very similar GUI figure 3 found at Applications Utilities ODBC Administrator Both unixODBC and iODBC provide GUIs which might be packaged sepa rately in binary distributions to create DSNs and i0DBC also has a web based DSN administrator UnixODBC s GUI is currently called ODBCConfig see figure 4 and there is a KDE control widget called
27. ern The details are driver specific but in most cases some_pattern can use wild cards with underscore matching a single character and percent matching zero or more characters Since underscore is a valid character in a table name it can be handled literally by preceding it by a backslash but it is rarely necessary to do so A table can be retrieved as a data frame by res lt sqlFetch ch table_name If it has many rows it can be retrieved in sections by res lt sqlFetch ch table_name max m res lt sqlFetchMore ch table name max m It is often necessary to reduce the data to be transferred we have seen how to subset rows but it can be more effective to restrict the columns or to return only rows meeting some conditions To find out what columns are available use sq1Columns for example gt sqlColumns ch USArrests TABLE_CAT TABLE_SCHEM TABLE_NAME COLUMN_NAME DATA_TYPE TYPENAME COLUMN_SIZE 1 ripley lt NA gt USArrests State 12 varchar 255 2 ripley lt NA gt USArrests Murder 8 double 15 3 ripley lt NA gt USArrests Assault 4 integer 10 4 ripley lt NA gt USArrests UrbanPop 4 integer 10 5 ripley lt NA gt USArrests Rape 8 double 15 Then an SQL Query can be used to return part of the table for example MySQL on Linux gt sqlQuery sh paste SELECT State Murder FROM USArrests WHERE Rape gt 30 ORDER BY Murder State Murder 1 Colorado 7 9 2 Arizona 8 1 3 California 9 0 4 Alaska
28. es The initial database is known as main and that used for temporary tables as temp e MySQL uses catalog to refer to a database In MySQUL s parlance schema is a little used synonym for database e PostgreSQL only allows a session to access one database and does not use catalog except to refer to the current database Version 7 3 introduced schemas users can create their own schemas with a CREATE SCHEMA query Tables are by default in the public schema and unqualified table names are searched for along a search path of schemas by default containing public e Oracle uses schemas as synonymous with owner also known as user There is no way for a user to create additional schemas that is not what CREATE SCHEMA does in Oracle e IBM DB2 uses schemas as name spaces for objects that may lie on different databases using aliases allows objects to be in more than one schema The initial current schema is named the same as the user SQLID in DB2 parlance but users can create additional schemas with CREATE SCHEMA statements e Microsoft SQL Server 2008 uses both catalog and schema catalog for the database and schema for the type of object e g sys for most of the system tables views and default dbo for user tables Further schemas can be created by users The default schema for a user can be set when the user is created and changed via ALTER USER Prior to SQL Server 2005 schema mea
29. es sell a driver for Mac OS X that covers some Excel spread sheets and flat files A connection to a specific database is called a Data Source Name or DSN SQL is a language for querying and managing data in databases see http en wikipedia org wiki SQL but there are close links between unixODBC and Easysoft and iODBC and OpenLink see http en wikipedia org wiki Database_Source_Name See Ap pendix B for how to set up DSNs on your system One of the greatest advantages of ODBC is that it is a cross platform client server design so it is common to run R on a personal computer and access data on a remote server whose OS may not even be known to the end user This does rely on suitable ODBC drivers being available on the client they are for the major cross platform DBMSs and some vendors provide bridge drivers so that for example a bridge ODBC driver is run on a Linux client and talks to the Access ODBC driver on a remote Windows machine ODBC provides an abstraction that papers over many of the differences between DBMSs That abstraction has developed over the years and RODBC works with ODBC version 3 This number describes both the API most drivers nowadays work with API 3 51 or 3 52 and capabilities The latter allow ODBC drivers to implement newer features partially or not at all so some drivers are much more capable than others in the main RODBC works with basic features ODBC is a superset of the ISO IE
30. h as tables and views within a database that are supported by some DBMSs often a separate schema is associated with each user and schema in ODBC 3 replaced owner in ODBC 2 In SQL 92 schemas are collected in a catalog which is often implemented as a database Where schemas are implemented there is a current schema used to find unqualified table names and tables in other schemas can be referred to within SQL queries using the schema table notation You can think of a schema as analogous to a name space it allows related objects to be grouped together without worrying about name clashes with other groups Some DBMSs will search for unqualified table names in a search path see the detailed descriptions below Note that schema is used in another sense in the database literature for the design of a database and in particular of tables views and privileges Here are some details of various DBMSs interpretations of catalog and schema current at the time of writing mid 2009 These descriptions are simplistic and in some cases experimental observations e SQLite uses dotted names for alternative databases that are attached lwhich is the usual plural in this technial usage athough schemata is more usual in English 13 by an ATTACH DATABASE command There is a search path of databases so it is only necessary to use the dotted name notation when there are tables of the same name on attached databas
31. ion of the quoting rules for names RODBC itself sends but sensible defaults are selected Users do need to be aware of the quoting issue when writing queries for sqlQuery themselves Note the underscore is a wildcard character in table names for some of the functions and so may need to be escaped by backslash at times Normally table names containing a period are interpreted as references to another schema see below this can be suppressed by opening the connec tion with argument interpretDot FALSE 2 4 Types of table The details are somewhat DBMS specific but tables usually means tables views or similar objects In some systems tables are physical objects files that actually store data Mimer calls these base tables For these other tables can be derived that present information to the user usually called views The principal dis tinctions between a base table and a view are MySQL Oracle and SQL Server backticks for MySQL for the Access and Excel convenience wrappers otherwise ANSI double quotes e Using DROP on a table removes the data whereas using it on a view merely removes the convenient access to a representation of the data e The access permission privilege of a view can be very different from those of a table this is commonly used to hide sensitive information A view can contain a subset of the information available in a single table or combine informatio
32. ir own data types and later mapped the stan dard SQL data types on to them although these may only be partially implemented Some DBMSs allow user defined data types for example enu merations Commonly used data types fall into a number of groups Character types Character types can be classified three ways fixed or variable length by the maximum size and by the character set used The most commonly used types are varchar for short strings of vari able length up to some maximum and char for short strings of fixed length usually right padded with spaces The value of short differs by DBMS and is at least 254 often a few thousand often other types will be available for longer character strings There is a sanity check which will allow only strings of up to 65535 bytes when reading this can be removed by recompiling RODBC Many other DBMSs have separate types to hold Unicode character strings often with names like nvarchar or wvarchar Note that cur rently RODBC only uses the current locale for character data which could be UTF 8 and will be on Mac OS X and in many cases on Linux and other Unix alikes but is never UCS 2 as used on Win dows So if character data is stored in the database in Unicode it the SQL names for these are CHARACTER VARYING and CHARACTER but these are too cumbersome for routine use will be translated with a possible loss of information in non Unicode locales This may change in fut
33. ith names remapped as necessary For the many options see the help page sqlSave works well when asked to write integer numeric and reasonable length character strings to the database It needs some help with other 8 which of course depends on the DBMS Almost all have an implementation of varchar types of columns in mapping to the DBMS specific types of column For some drivers it can do a good job with date and date time columns in oth ers it needs some hints and e g for Oracle dates are stored as date times The files in the RODBC tests directory in the sources and the installed file tests R provide some examples One of the options is the fast argument the default is fast TRUE which transfers data in binary format the alter native is fast FALSE which transfer data as character strings a row at a time this is slower but can work better with some drivers and worse with others The other main tool for writing is sqlUpdate which is used to change rows in an existing table Note that RODBC only does this in a simple fashion and on up market DBMSs it may be better to set cursors and use direct SQL queries or at least to control transactions by calls to odbcSetAutoCommit and odbcEndTran The basic operation of sqlUpdate is to take a data frame with the same column names up to remapping as some or all of the columns of an existing table the values in the data frame are then used either to replace entries or to create new rows
34. ke changes If your application requires special handling of non English text Introduction press Advanced Language Data Source Advanced Language Database Always include views in table lists Conclusion m Top row contains column names C Save long running queries to the log file Users ripley Query log Choose Long query time milliseconds 30000 ODBC for Access NOTE this driver supports multi table SELECT statements Statements that and xls txt and csv files modify the database such as CREATE UPDATE and INSERT are not supported in the current version of the driver actualtechnologies Cna Comm Figure 3 Top The main ODBC Administrator dialog box from a Mac OS X system Bottom A page of the dialog box to specify a DSN for the Actual Technologies Access Excel driver 28 gt ODBC Data Source Administrator lt gannetstats oxac v A System DSN Ele DSN Drivers stats Advanced Name Description Driver Add sqlite3 sqlite3 sqlite3 test myodbc MySQL testpg testpg PostgreSQL This allows you to configure data access without having to be the o User data source configuration is stored in your home directory system administrator Ps 5 Data Source Properties edit lt gannet stats o a R v x Rk Name sqlite Description Driver Database nmpimysqitesdb F Timeout 100000 StepAPI ShortNames no ooo NoCreat SyncPragma NORMAL D wa
35. lsx xlsm Remove MS Access Database Microsoft Access Driver mdb accdb myodbe MySQL ODBC 3 51 Driver Configure sqlite3 SQLite3 ODBC Driver Lente testacc Microsoft Access Driver mdb testdb3 MySQL ODBC 3 51 Driver testdb5 MySQL ODBC 5 1 Driver An ODBC User data source stores information about how to connect to the indicated data provider A User data source is only visible to you and can only be used on the current machine Create New Data Source Select a driver for which you want to set up a data source gt Microsoft Text Treiber txt csv Microsoft Visual FoxPro Driver Microsoft Visual FoxPro Treiber MySQL ODBC 3 51 Driver MySQL ODBC 5 1 Driver SQL Server SQLite ODBC UTF 8 Driver SQLite ODBC Driver SQLite3 ODBC Driver lt mammann mm nle lt IL lt Back Cancel Figure 2 Top The main Data Sources ODBC dialog box from a Windows XP system Bottom The dialog box to select a driver that comes up when the Add button is clicked 27 OOO ODBC Administrator User DSN System DSN Drivers Tracing Connection Pooling About Name Description Driver E Add y hills xls Actual Access Remove Configure An ODBC System data source stores information about how to connect to the indicated data provider A System data source is visible to all users and processes on this machine ti Enter the database information ie Click the lock to ma
36. n from two or more tables Further some DBMSs distinguish between tables and views generated by ordinary users and system tables used by the DBMS itself Where present this distinction is reflected in the result of sqlTable calls Some DBMSs support synonyms and or aliases which are simply alternative names for an existing table view synonym often those in other schemas see below Typically tables views synonyms and aliases share a name space and so must have a name that is unique in the enclosing schema where schemas are implemented 3 Writing to a Database To create or update a table in a database some more details need to be considered For some systems all table and column names need to be lower case e g PostgreSQL MySQL on Windows or upper case e g some versions of Oracle To make this a little easier the odbcConnect function allows a remapping of table names to be specified and this happens by default for DBMSs where remapping is known to be needed The main tool to create a table is sqlSave It is safest to use this after having removed any existing table of the same name which can be done by sqlDrop ch table_name errors FALSE Then in the simplest usage sqlSave ch some_data_frame creates a new table whose name is the name of the data frame remapped to upper or lower case as needed and with first column rownames the row names of the data frame and remaining columns the columns of the data frame w
37. nf Inf or NaN but they often can Other numeric types It is common to store decimal quantities in databases e g currency amounts and types 2 and 3 are for deci mals Some DBMSs have specialized types to handle currencies e g money in SQL Server Decimal types have a precision the maximum number of significant decimal digits and scale the position of the decimal point numeric and decimal are usually synonymous but the distinction in the stan dards is that for numeric the precision is exact whereas for decimal the DBMS can use a larger value than that specified In Oracle the FLOAT type is a decimal and not a binary type 10 Some DBMSs have a type integer p to represent up to p decimal digits and this may or may not be distinct from decimal p 0 DBMSs do not necessarily fully implement decimal types e g MySQL currently stores them in binary and used to store them as character strings Dates and times The handling of dates and times is very much specific to the DBMS Some allow fractional seconds in date times and some do not some store timezones with date times or always use UTC and some do not and so on Usually there are also types for time intervals All such types are transferred as character strings in RODBC Binary types These are less common and unsupported by RODBC prior to version 1 3 0 They parallel character types in that they are a sequence of bytes of fixed or variable length sometimes with a
38. nformation for end users in the INFORMATION_SCHEMA database much more extensively as from MySQL 5 1 Some of the non standard behaviour can be turned off e g starting MySQL with sql mode ANSI gives closer conformance to the standard and this can be set for a single session by SET SESSION sql_mode ANSI To change just the behaviour of quotes to use double quotes in place of backticks replace ANSI by ANSI_QUOTE The maximum size of a char column is 255 characters That of a varchar column is up to 65535 characters but there is a limit of 65535 bytes on the total size of a row and those with a maximum of 255 or less are stored more efficiently Types text mediumtext and longtext can hold more and are not subject to the row size limit text has default maximum size 65535 the default RODBC limit on transfers There are binary varbinary and blob types which are very similar to their character counterparts but with lengths in bytes PostgreSQL Table pg_tables lists all tables in all schemas you probably want to filter on tableowner current_user e g gt sqlQuery channel select from pg_tables where tableowner ripley schemaname tablename tableowner tablespace hasindexes hasrules hastriggers 1 public dtest ripley NA 0 0 0 There are both ANSI and Unicode versions of the ODBC driver on Windows they provide many customizations One of these is read only access another is if system tables are reported b
39. nt user and the search path for unqualified names was the database user then dbo e The Microsoft Excel and Access ODBC drivers do not use schemas but do use catalog to refer to other database spreadsheet files e Mimer www mimer com uses schemas which are normally the same as users which it calls IDENTs but users can create additional schemas with CREATE SCHEMA statements There are also system schemas Mimer uses schemata as the plural of schema It is often possible to use sqlTables to list the available catalogs or schemas see its help page for the driver specific details and may be subsequently detached by a DETACH DATABASE command 14 RODBC usually works with tables in the current schema but unless the con nection was opened with interpretDot FALSE most functions will at tempt to interpret the dotted name notation The interpretation depends on the DBMS the SQL 92 meaning is schema table and this is accepted by PostgreSQL Microsoft SQL Server Oracle DB2 and Mimer However MySQL uses database table and the functions try that interpretation if they recognize a MySQL driver Some DBMSs allow more than two com ponents but these are not currently supported by the RODBC functions Functions sqlTables sqlColumns and sqlPrimaryKeys have arguments catalog and schema which in principle allow tables in other schemas to be listed or examined however these are only partially implemented in many
40. qlColumns is used to set the SQL_ATTR_METADATA_ID attribute of the statement handle to be true All the functions that create a result set call C function cachenbind This allocates buffers under the colData pointer and binds the result set to them by SQLBindCol Then when sqlGetResults calls the C function SQLFetch or SQLFetchScrol1l the results for one or more up to MAX_ROWS_FETCH 1024 rows are loaded into the buffers and then copied into R vectors Prior to RODBC 1 3 0 the default was to fetch a row at a time but it is now to fetch up to 100 rows at a time Entries rowsArraySize and rowsFetched are used to indicate how many rows were requested and how many were available Since e g sqlFetch allows a maximum number of rows to be returned in the data frame rowsUsed indicates how many of the rows last fetched have so far been returned to R The buffers are part of the ColData entry which is an array of COLUMNS structures one of each column in the result set These have the form typedef struct cols SQLCHAR ColName 256 SQLSMALLINT NameLength SQLSMALLINT DataType SQLULEN ColSize SQLSMALLINT DecimalDigits SQLSMALLINT Nullable char pData int datalen odbcQuery sqlColumns sqlPrimaryKeys sqlTables and sqlTypeInfo 33 SQLDOUBLE RData MAX_ROWS_FETCH SQLREAL R4Data MAX_ROWS_FETCH SQLINTEGER IData MAX_ROWS_FETCH SQLSMALLINT I2Data MAX_ROWS_FETCH SQLLEN IndPtr MAX_ROWS_FETCH COLUMNS The
41. t on tables in specified databases 15 ODBC drivers e g for SQL Server Oracle allow the locale NLS to be used for numeric values to be selected for the connection The other internationalization issue is the character encoding used When R and the DBMS are running on the same machine this is unlikely to be an issue and in many cases the ODBC driver has some options to translate character sets SQL is an ANSI US standard and DBMSs tended to assume that character data was ASCII or perhaps 8 bit More recently DBMSs have started to optionally or by default to store data in Unicode which unfortunately means UCS 2 on Windows and UTF 8 elsewhere So cross OS solutions are not guaranteed to work but most do Encoding issues are best resolved in the ODBC driver or in DBMS settings In the unusual case that this cannot be done the DBMSencoding argument to odbcDriverConnect allows for recoding when sending data to or from the ODBC driver and thence the DBMS 7 Excel Drivers The Microsoft Excel ODBC driver Windows only has a number of pecu liarities which mean that it should be used with care It seems that its concept of a table is principally a named range It treats worksheets are system tables and append a dollar to their name making then non standard SQL table names the quoting convention used is to enclose such names in square brackets Column names are taken as the first row of the named range worksheet
42. ues including that it seems not to support dropping tables Christian Werner s SQLite ODBC driver was easy to install from the sources and works correctly Oracle Tables cat user_table and user_catalog contain useful information on tables Information on columns is in all_tab_columns e g gt sqlQuery channel Select from all_tab_columns where table_name USArrests OWNER TABLE_NAME COLUMN_NAME DATA_TYPE DATA_TYPE_MOD 1 RIPLEY USArrests State VARCHAR2 NA 2 RIPLEY USArrests Murder FLOAT NA 3 RIPLEY USArrests Assault NUMBER NA 4 RIPLEY USArrests UrbanPop NUMBER NA 5 RIPLEY USArrests Rape FLOAT NA The Windows ODBC driver we tested had an option for a read only con nection Oracle s character data types are CHAR VARCHAR2 character set specified when the database was created and NCHAR NVARCHAR2 Unicode as well as CLOB and NCLOB for large character strings For the non Unicode types the units of length are either bytes or charactor set as a default for the 19 database but can be overriden by adding a BYTE or CHAR qualifier The limits are 4000 bytes apart from for CLOB and NCLOB which have very high limits There are RAW and BLOB data types DB2 Schema syscat contains many views with information about tables for example view syscat tables lists all tables and gt sqlQuery channel select from syscat columns where tabname USArrests TABSCHEMA TABNAME COLNAME COLNO TYPESCHEMA TYPENAME LE
43. unixODBC and iODBC store information on drivers in configura tion files normally system wide in etc odbcinst ini and per user in odbcinst ini However the system location can vary and on systems with unixODBC can be found by at the Unix command line by one of odbcinst j odbc_config odbcinstini For iODBC use iodbc_config on Mac OS X the system location is Library ODBC odbcinst ini The format can be seen from figure 1 unixODBC allows Driver64 here to allow for different paths on 32 bit and 64 bit platforms sharing a file sys tem The MySQL and PostgreSQL drivers were installed from the Fedora RPMs mysql connector odbc and postgresql odbc and also from the mysql connector odbc RPM in the MySQL distribution which inserted the entry in the driver file The MySQL manual gives detailed information including screenshots of installing its drivers and setting up DSNs that may also be informative to users of other DBMSs 24 cat etc odbcinst ini MySQL Description ODBC 3 51 26 for MySQL Driver usr 1ib64 libmyodbc3 so FileUsage 1 MySQL ODBC 5 1 Driver Description ODBC 5 1 05 for MySQL Driver usr lib64 libmyodbc5 so UsageCount 1 PostgreSQL Description ODBC for PostgreSQL Driver usr 1ib64 psqlodbc so FileUsage 1 sqlite3 Description sqliteodbc Driver usr local 1ib64 libsqlite3o0dbc so Setup usr local 1ib64 libsqlite3o0dbc so FileUsage 1 Figure 1 A system ODBC driv
44. ure versions of RODBC Some DBMSs such as PostgreSQL and SQL Server allow variable length character strings of length only limited by resources These do not fit well with the ODBC model that requires buffers to be allocated to transfer character data and so such types may be subjected to a fixed limit or not work at all Integer types Most DBMSs have types for 32 bit integer synomyn int and 16 bit smallint integers Some including MySQL also have unsigned versions and 1 bit 8 bit and 64 bit integer types these fur ther types would usually be transferred as character strings and con verted on reading to an integer or double vector Type names int2 int4 and int8 are common as synonyms for the basic type names The SQL standard does not require integer and smallint to be bi nary rather than decimal types but they almost always are binary Note that 64 bit integers will be transferred as character strings and read by sqlGetResults as character vectors or for 2 lt z lt 253 as double vectors Floating point types The basic SQL floating point types are 8 and 7 for double and single precision binary types The SQL names are double precision and real but beware of the variety of names Type 6 is float in the standard but is used by some DBMSs for single precision and by some for double precision the forms float 24 and float 53 are also commonly supported You should not assume that these types can store I
45. y sqlTables The default size of a varchar column is unlimited but those with maximum length of 126 bytes or less are stored more efficiently However the ODBC interface has limits which can be set in the configuration options These include the maximum sizes for varchar default 254 and longvarchar de fault 8190 and how to handle unknown column sizes default as the max imum and whether Text is taken as varchar or longvarchar which affects the reported maximum size for a varchar column There is a single binary data types bytea 18 SQLite These comments are only about SQLite 3 x Table sqlite_master lists tables and indices and the sql column gives the SQL command used E g gt tmp lt sqlQuery channel select from sqlite_master gt tmp sql lt substr tmp sql 1 16 gt tmp type name tbl_name rootpage sql 1 table USArrests USArrests 2 CREATE TABLE US 2 index sqlite_autoindex_USArrests_1 USArrests 4 lt NA gt My current versions of Christian Werner s SQLite ODBC driver store char acter data in the current locale s charset e g UTF 8 on Unix alikes and by default in Unicode UCS 2 on Windows unless de selected in the DSN configuration The default collation for text data is byte by byte comparisons so avoid comparing non ASCII character data in SQLite Actual Technologies sell an SQLite driver for Mac OS X which requires believeNRows FALSE and has a number of other iss
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