You receive a "Query is too complex" error message when you try to update or to delete a record of a CRecordset object in Visual C++

CAUSE

The error occurs when the cursor library is loaded and the recordset retrieved by the CRecordset is opened as a snapshot object that contains more than 40 bound columns.

By default, the cursor library is loaded when a CRecordset is opened. MFC snapshots perform positioned updates and deletes by using the ODBC SQL WHERE CURRENT OF syntax. The cursor library changes the WHERE CURRENT OF clause to a full WHERE clause using all the columns in the recordset.

For example, the MFC Database classes might create the following SQL statement when updating a record:

   Update table1
   SET column1=?
   WHERE CURRENT OF XXXXX
				

The cursor library knows which record the application is currently positioned at and converts the WHERE CURRENT OF clause into a WHERE clause that will update the current record only. For example, assume the recordset has three columns. The cursor library changes the SQL statement to:

   Update table1
   SET column1=?
   WHERE column1=<current value> AND column2=<current value> AND
     column3 =<current value>
				

Here <current value> represents the value of that column before the update is performed.

You can see that more than 40 columns in a CRecordset will cause more than 40 AND predicates in the WHERE clause. The helpfile for the ODBC desktop drivers (ODBCJET.HLP) states in the SQL limitations section that no more than 40 AND predicates are supported. Thus, the SQL statement is too complex.

NOTE: Long binary columns (those using RFX_LongBinary) are not bound and do not count against the 40-column limit. However, an MFC ODBC application that references the RFX_LongBinary function may encounter this error when the recordset is opened. This is because the cursor library precedes calls to SQLGetData with the execution of a SELECT statement with a WHERE clause as described above.