SQLGetDescField

Article
01/10/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)

The SQL Server Native Client ODBC driver exposes driver-specific descriptor fields for the implementation row descriptor (IRD) only. Within the IRD, SQL Server descriptor fields are referenced through driver-specific column attributes. For information about a complete list of available driver-specific descriptor fields, see SQLColAttribute.

Descriptor fields that contain column identifier strings are often zero-length strings. All SQL Server-specific descriptor field values are read-only.

Like attributes retrieved with SQLColAttribute, descriptor fields that report row-level attributes (such as SQL_CA_SS_COMPUTE_ID) are reported for all columns in the result set.

SQLGetDescField and Table-Valued Parameters

SQLGetDescField can be used to get values for extended attributes of table-valued parameters and table-valued parameter columns. For more information about table-valued parameters, see Table-Valued Parameters (ODBC).

SQLGetDescField Support for Enhanced Date and Time Features

For information about the descriptor fields available with the new date/time types, see Parameter and Result Metadata.

For more information, see Date and Time Improvements (ODBC).

Beginning in SQL Server 2012 (11.x), SQLGetDescField can return SQL_C_SS_TIME2 (for time types) or SQL_C_SS_TIMESTAMPOFFSET (for datetimeoffset) instead of SQL_C_BINARY, if your application uses ODBC 3.8.

SQLGetDescField Support for Large CLR UDTs

SQLGetDescField supports large CLR user-defined types (UDTs). For more information, see Large CLR User-Defined Types (ODBC).

SQLGetDescField Support for Sparse Columns

SQLGetDescField can be used to query the new IRD field SQL_CA_SS_IS_COLUMN_SET to determine if a column is a column_set column.

For more information, see Sparse Columns Support (ODBC).

Example

typedef struct tagCOMPUTEBYLIST  
    {  
    SQLSMALLINT nBys;  
    SQLSMALLINT aByList[1];  
    } COMPUTEBYLIST;  
typedef COMPUTEBYLIST* PCOMPUTEBYLIST;   
  
SQLHDESC    hIRD;   
SQLINTEGER  cbIRD;   
SQLINTEGER  nSet = 0;   
  
// . . .  
// Execute a statement that contains a COMPUTE clause,  
//  then get the descriptor handle of the IRD and  
//  get some IRD values.  
  
SQLGetStmtAttr(g_hStmt, SQL_ATTR_IMP_ROW_DESC,  
    (SQLPOINTER) &hIRD, sizeof(SQLHDESC), &cbIRD);  
  
// For statement-wide column attributes, any  
//  descriptor record will do. You know that 1 exists,  
//  so use it.  
SQLGetDescField(hIRD, 1, SQL_CA_SS_NUM_COMPUTES,  
    (SQLPOINTER) &nComputes, SQL_IS_INTEGER, &cbIRD);  
  
if (nSet == 0)  
    {  
    SQLINTEGER      nOrderID;  
  
    printf_s("Normal result set.\n");  
  
    for (nCol = 0; nCol < nCols; nCol++)  
        {  
        SQLGetDescField(hIRD, nCol+1,  
            SQL_CA_SS_COLUMN_ORDER,  
            (SQLPOINTER) &nOrderID, SQL_IS_INTEGER,  
            &cbIRD);  
  
        if (nOrderID != 0)  
            {  
            printf_s("Col in ORDER BY, pos: %ld",  
                nOrderID);  
            }  
            printf_s("\n");  
        }  
  
    printf_s("\n");  
    }  
else  
    {  
    PCOMPUTEBYLIST  pByList;  
    SQLSMALLINT     nBy;  
    SQLINTEGER      nColID;  
  
    printf_s("Computed result set number: %lu\n",  
        nSet);  
  
    SQLGetDescField(hIRD, 1, SQL_CA_SS_COMPUTE_BYLIST,  
        (SQLPOINTER) &pByList, SQL_IS_INTEGER,  
        &cbIRD);  
  
    if (pByList != NULL)  
        {  
        printf_s("Clause ordered by columns: ");  
        for (nBy = 0; nBy < pByList->nBys; )  
            {  
            printf_s("%u", pByList->aByList[nBy]);  
            nBy++;  
  
            if (nBy == pByList->nBys)  
                {  
                printf_s("\n");  
                }  
            else  
                {  
                printf_s(", ");  
                }  
            }  
        }  
    else  
        {  
        printf_s("Compute clause set not ordered.\n");  
        }  
  
    for (nCol = 0; nCol < nCols; nCol++)  
        {  
        SQLGetDescField(hIRD, nCol+1,  
            SQL_CA_SS_COLUMN_ID, (SQLPOINTER) &nColID,  
            SQL_IS_INTEGER, &cbIRD);  
        printf_s("ColumnID: %lu, nColID);  
        }  
    printf_s("\n");  
    }  
  
if (SQLMoreResults(g_hStmt) == SQL_SUCCESS)  
    {  
    // Determine the result set indicator.  
    SQLGetDescField(hIRD, 1, SQL_CA_SS_COMPUTE_ID,  
        (SQLPOINTER) &nSet, SQL_IS_INTEGER, &cbIRD);  
    }