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

C Interval Structure

Each of the C interval data types listed in the "C Data Types" section uses the same structure to contain the interval data. When SQLFetch, SQLFetchScroll, or SQLGetData is called, the driver returns data into the SQL_INTERVAL_STRUCT structure, uses the value that was specified by the application for the C data types (in the call to SQLBindCol, SQLGetData, or SQLBindParameter) to interpret the contents of SQL_INTERVAL_STRUCT, and populates the interval_type field of the structure with the enum value corresponding to the C type. Note that drivers do not read the interval_type field to determine the type of the interval; they retrieve the value of the SQL_DESC_CONCISE_TYPE descriptor field. When the structure is used for parameter data, the driver uses the value specified by the application in the SQL_DESC_CONCISE_TYPE field of the APD to interpret the contents of SQL_INTERVAL_STRUCT, even if the application sets the value of the interval_type field to a different value.

This structure is defined as follows:

typedef struct tagSQL_INTERVAL_STRUCT
{
   SQLINTERVAL interval_type; 
   SQLSMALLINT interval_sign;
   union {
         SQL_YEAR_MONTH_STRUCT   year_month;
         SQL_DAY_SECOND_STRUCT   day_second;
         } intval;
} SQL_INTERVAL_STRUCT;
typedef enum 
{
   SQL_IS_YEAR = 1,
   SQL_IS_MONTH = 2,
   SQL_IS_DAY = 3,
   SQL_IS_HOUR = 4,
   SQL_IS_MINUTE = 5,
   SQL_IS_SECOND = 6,
   SQL_IS_YEAR_TO_MONTH = 7,
   SQL_IS_DAY_TO_HOUR = 8,
   SQL_IS_DAY_TO_MINUTE = 9,
   SQL_IS_DAY_TO_SECOND = 10,
   SQL_IS_HOUR_TO_MINUTE = 11,
   SQL_IS_HOUR_TO_SECOND = 12,
   SQL_IS_MINUTE_TO_SECOND = 13
} SQLINTERVAL;

typedef struct tagSQL_YEAR_MONTH
{
   SQLUINTEGER year;
   SQLUINTEGER month; 
} SQL_YEAR_MONTH_STRUCT;

typedef struct tagSQL_DAY_SECOND
{
   SQLUINTEGER day;
   SQLUINTEGER hour;
   SQLUINTEGER minute;
   SQLUINTEGER second;
   SQLUINTEGER fraction;
} SQL_DAY_SECOND_STRUCT;

The interval_type field of the SQL_INTERVAL_STRUCT indicates to the application what structure is held in the union and also what members of the structure are relevant. The interval_sign field has the value SQL_FALSE if the interval leading field is unsigned; if it is SQL_TRUE, the leading field is negative. The value in the leading field itself is always unsigned, regardless of the value of interval_sign. The interval_sign field acts as a sign bit.