MDAC 2.5 SDK - ODBC Programmer's Reference
Appendix D: Data Types

Appendix D: 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 SQL-92 standard. For each SQL data type specified in the SQL-92 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 SQL-92 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 includes the following sections:

• Using Data Type Identifiers
  
  
• SQL Data Types
  
  
• C Data Types
  
  
• Data Type Identifiers and Descriptors
  
  
• Pseudo-Type Identifiers
  
  
• Transferring Data in Its Binary Form
  
  
• Guidelines for Interval and Numeric Data Types
  
  
• Constraints of the Gregorian Calendar
  
  
• Column Size, Decimal Digits, Transfer Octet Length, and Display Size
  
  
• 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.