Overview of Data Types

ODBC defines two sets of data types: SQL data types and C data types. SQL data types indicate the data type of data stored at the data source. C data types indicate the data type of data stored in application buffers.

SQL data types are defined by each DBMS in accordance with the SQL92 standard. For each SQL data type specified in the SQL92 standard, ODBC defines a type identifier, which is a #define value that is passed as an argument in ODBC functions or returned in the metadata of a result set. The only SQL92 data types not supported by ODBC are BIT (the ODBC SQL_BIT type has different characteristics), BIT_VARYING, TIME_WITH_TIMEZONE, TIMESTAMP_WITH_TIMEZONE, and NATIONAL_CHARACTER. Drivers are responsible for mapping data source – specific SQL data types to ODBC SQL data type identifiers and driver-specific SQL data type identifiers. The SQL data type is specified in the SQL_DESC_CONCISE_TYPE field of an implementation descriptor.

ODBC defines the C data types and their corresponding ODBC type identifiers. An application specifies the C data type of the buffer that will receive result set data by passing the appropriate C type identifier in the TargetType argument in a call to SQLBindCol or SQLGetData. It specifies the C type of the buffer containing a statement parameter by passing the appropriate C type identifier in the ValueType argument in a call to SQLBindParameter. The C data type is specified in the SQL_DESC_CONCISE_TYPE field of an application descriptor.

Note   There are no driver-specific C data types.

Each SQL data type corresponds to an ODBC C data type. Before returning data from the data source, the driver converts it to the specified C data type. Before sending data to the data source, the driver converts it from the specified C data type.

This appendix discusses the following:

• ODBC SQL data types
  
  
• ODBC C data types
  
  
• Interval data types
  
  
• Numeric literals
  
  
• Data type identifiers, including pseudo-type identifiers, transferring data in its binary form, and information on descriptors
  
  
• Column size, decimal digits, transfer octet length, and display size of SQL data types
  
  
• Converting data from SQL to C data types
  
  
• Converting data from C to SQL data types

For an explanation of ODBC data types, see “Data Types in ODBC” in Chapter 4, “ODBC Fundamentals.” For information about driver-specific SQL data types, see the driver’s documentation.