ODBC API Reference

Obtaining Parameter Description

SQLDescribeParam is a function in the ODBC API. It is used to obtain the description of parameters related to prepared SQL statements (for example, calling SQLPrepare). It can return metadata such as the type, size, and whether NULL values are allowed for parameters, which is useful for dynamically building SQL statements and binding parameters.

Prototype

SQLRETURN SQLDescribeParam(  
      SQLHSTMT        StatementHandle,  
      SQLUSMALLINT    ParameterNumber,  
      SQLSMALLINT    *DataTypePtr,  
      SQLULEN        *ParameterSizePtr,  
      SQLSMALLINT    *DecimalDigitsPtr,  
      SQLSMALLINT    *NullablePtr);

**Table 1** Parameters of SQLDescribeParam
Parameter	Description	Difference
StatementHandle	Statement handle.	-
ParameterNumber	Parameter marker number, starting with 1 and increasing in ascending order.	-
DataTypePtr	Points to the data type of the returned parameter.	In MySQL, ODBC returns SQL_VARCHAR for any type. In GaussDB, ODBC returns the data type to an application based on that returned by the kernel.
ParameterSizePtr	Points to the size of the returned parameter.	If MySQL allows the ODBC driver to use a larger data packet for data transmission, 24M is returned. Otherwise, 255 is returned. In GaussDB, ODBC returns the parameter size based on the actual type.
DecimalDigitsPtr	Points to the number of decimal digits of the returned parameter.	-
NullablePtr	Points to whether NULL values are allowed for the returned parameter.	In MySQL, ODBC directly returns SQL_NULLABLE_UNKNOWN. In GaussDB, ODBC directly returns SQL_NULLABLE.