FIX: SQLDescribeCol Returns Wrong Column Size in a Union Query with Parameters

• The query consists of a union of two or more SELECT statements.
• One of the WHERE clauses contains parameters.
• The first of the two unioned queries returns a constant for a column (for example, SELECT 'ABC') and the other returns a column (for example, SELECT col1).

1. Compile the query into a stored procedure that contains parameters.
2. Reverse the order of the SELECT statements in the union query so that the constant field is in the latter SELECT statement.
3. Call SQLBindParameter before you call SQLDescribeCol.

SELECT 'AB' FROM a UNION SELECT col1 FROM b WHERE 1=?
				

Steps to Reproduce Behavior

1. Create the following tables on Microsoft SQL Server:

   CREATE TABLE [dbo].[a] (
   	[a] [char] (20) NULL 
   ) ON [PRIMARY]
   GO
   
   CREATE TABLE [dbo].[b] (
   	[col1] [char] (20) NULL 
   ) ON [PRIMARY]
   GO
   					

2. Paste the following code in a Microsoft Visual C++ console application (note that you must change the data source name, user ID, and password to correspond to your situation):

   #include <windows.h>
   #include <sql.h>
   #include <sqlext.h>
   #include <sqltypes.h>
   #include <conio.h>
   #include <Odbcss.h>
   #include <stdio.h>
   
   void HandleError(SQLHANDLE	hHandle, SQLSMALLINT hType, RETCODE RetCode)
   {
       SQLSMALLINT	iRec = 0;
       SQLINTEGER	iError;
       TCHAR	szMessage[1000];
       TCHAR	szState[SQL_SQLSTATE_SIZE + 1];
   
       if (RetCode == SQL_INVALID_HANDLE)
       {
   	fprintf(stderr,"Invalid handle!\n");
   	return;
       }
   
       while (SQLGetDiagRec(hType, hHandle, ++iRec,(SQLCHAR *)szState, <BR/>
              &iError,(SQLCHAR *)szMessage, (SQLSMALLINT)(sizeof(szMessage)/ 
              sizeof(TCHAR)),(SQLSMALLINT *)NULL) == SQL_SUCCESS)
       {
            fprintf(stderr,TEXT("[%5.5s] %s (%d)\n"),szState,szMessage,iError);
       }
   
   }
   
   void main(int argc, char* argv[])
   {
       SQLHENV henv;
       SQLHDBC hdbc;
       SQLHSTMT hstmt;
       SQLRETURN nstatus;
       
       //For clarity, do not check the return codes in some cases.
       nstatus = SQLAllocHandle(SQL_HANDLE_ENV,NULL,&henv);
       nstatus = SQLSetEnvAttr(henv,SQL_ATTR_ODBC_VERSION,(SQLPOINTER) SQL_OV_ODBC3,0);
       nstatus = SQLAllocHandle(SQL_HANDLE_DBC,henv,&hdbc);
   
       nstatus = SQLConnect(hdbc, (SQLCHAR*) "<dsn name>", SQL_NTS, 
                            (SQLCHAR*) "<user id>", SQL_NTS, (SQLCHAR*) "<password>", SQL_NTS);
       if (nstatus != SQL_SUCCESS && nstatus != SQL_SUCCESS_WITH_INFO)
       {
   	HandleError(hdbc,SQL_HANDLE_DBC,nstatus);
   	return;
       }
   
       nstatus = SQLAllocHandle(SQL_HANDLE_STMT,hdbc,&hstmt);
       nstatus = SQLPrepare(hstmt,(SQLCHAR*) "SELECT 'AB' FROM a UNION SELECT col1 FROM b WHERE col1= ?", SQL_NTS);
   
       if (nstatus != SQL_SUCCESS)
       {
   	HandleError(hstmt,SQL_HANDLE_STMT,nstatus);
   	return;
       }
   	
       SQLCHAR szCol[255];
       SQLUINTEGER colSize;
       SQLSMALLINT slen, dataType, decDigits, Nullable;
       nstatus = SQLDescribeCol(hstmt, 1, szCol, 255, &slen, &dataType, &colSize, &decDigits, &Nullable);
   	
       if (nstatus != SQL_SUCCESS)
       {
   	HandleError(hstmt,SQL_HANDLE_STMT,nstatus);
   	return;
       }
   
       //The following line prints "2" as the column size. It should print "20".
       printf("Column size reported is: %d\n", colSize);
       SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
       SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
       SQLFreeHandle(SQL_HANDLE_ENV, henv);
   }
   					

3. Compile the code.