HOWTO: Update More Than 40 fields in an Access (Jet) Database

ID: Q192716

The information in this article applies to:

Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0
Microsoft Data Access Components versions 1.5, 2.0, 2.1 SP2

SUMMARY

The following error occurs when using RDO or ADO to update data in an Access (Jet) database:

Query is too complex

Due to a limitation of the Jet database engine, this error can occur if the recordset to be updated contains more than 40 fields.

Using the Jet 3.51 engine, the error occurs if the recordset to be updated contains more than 50 fields. With the Jet 4.0 engine and later, the error occurs if the recordset to be updated contains more than 99 fields.

Using the Jet 4.0 engine and later, you may also see the errors:

Expression too complex

-or-

Too many defined fields

This article describes the problem scenario, the Jet limitation, and several workarounds.

MORE INFORMATION

When executing the Update() or BatchUpdate() methods of RDO's rdoResultset object, or the Update() or UpdateBatch() methods of ADO's Recordset object, the ODBC error S1000 "Query is too complex" (Visual Basic run-time error 40002) occurs. An error with the same description occurs using the Microsoft Jet OLE DB providers versions 3.51 and later.

This behavior occurs because the default behavior of ADO and RDO is to use each field in the recordset to determine the record to be updated on the server. That is, when the update is attempted, a SQL Update query is sent to the server. Part of this query is a WHERE clause that is used to identify the record to be updated. An AND clause appears within the WHERE clause for each field to be used in that identification. Updating a recordset with more than 40 fields involves a WHERE clause with more than 40 ANDs.

The Jet engine allows only 40 AND clauses within a SQL WHERE or HAVING clause. Jet 3.51 increased this limit to 50 AND clauses, and Jet 4.0 increased the limit to 99 AND clauses. The Access engine returns a "Query is too complex" error when it encounters such a SQL statement. See the REFERENCES section of this article for more information.

There are several ways to avoid this behavior:

For new applications, use DAO when working with Access databases. DAO was designed for this purpose, and will not issue a SQL query to perform the update. Note that RDO and especially ADO were designed to operate efficiently with many other types of databases and are recommended for applications that will interact with various servers or that will be upsized in the future to use Microsoft SQL Server, for example.

When opening the recordset to be updated (such as the RDO OpenResultset or ADO OpenRecordset methods), select specific, and 40 or fewer fields.

Use a server-side cursor:

To do this in ADO, set the CursorLocation location property of the Recordset object to adUseServer before opening the Recordset:


         ...
         Dim rs As ADODB.Recordset
         Set rs = New ADODB.Recordset
         rs.CursorLocation = adUseServer
         rs.Open ...
            ...

In RDO, set the CursorDriver property of the rdoEnvironment object before calling the OpenConnection() method:


         ...
         Dim eng As RDO.rdoEngine
         Dim cn As RDO.rdoConnection
         Dim env As RDO.rdoEnvironment
         Dim rs As RDO.rdoResultset

         Set eng = New rdoEngine
         Set env = eng.rdoCreateEnvironment(...)
         env.CursorDriver = rdUseServer
         Set cn = env.OpenConnection(...)
         Set rs = cn.OpenResultset(...)
         ...

Ensure that a unique key is used to identify the record to be updated, rather than the default behavior of using every field. A unique key (though not necessarily a primary key) must be defined in the underlying recordset for this technique to work.
- To do this in ADO (this will not work in versions prior to ADO 2.0), set the Recordset object's "Update Criteria" property to adCriteriaKey. This will work both for the Update() and UpdateBatch() methods:
- For RDO, use the ClientBatch cursor library and ensure that the Resultset object's UpdateCriteria property is not set to rdCriteriaAllCols. By default, this property is set to rdCriteriaKey, which will cause the use of the primary key to determine the row(s) to be updated on the server:

REFERENCES

For additional information, please see the following article in the Microsoft Knowledge Base:

Q92690 ACC: Limit on ANDs in SQL Select Statement

Additional query words:

Keywords : kbAccess kbADO150 kbADO200 kbDatabase kbJET kbRDO200 kbVBp500 kbVBp600 kbGrpVBDB kbGrpMDAC kbDSupport kbADO210sp2
Version : WINDOWS:1.5,2.0,2.1 SP2,5.0,6.0
Platform : WINDOWS
Issue type : kbhowto