Microsoft KB Archive/192716

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

Article ID: 192716

Article Last Modified on 3/14/2005

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APPLIES TO


 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition
 * Microsoft Data Access Components 1.5
 * Microsoft Data Access Components 2.0
 * Microsoft Data Access Components 2.1 Service Pack 2

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This article was previously published under Q192716



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

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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: ...        Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.CursorLocation = adUseClient rs.Properties("Update Criteria").Value = adCriteriaKey rs.Open ...        ... </li>  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: ...        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 = rdUseClientBatch Set cn = env.OpenConnection(...) Set rs = cn.OpenResultset(...) rs.Edit ...        rs.UpdateCriteria = rdCriteriaKey rs.Update ...                           </li></ul> </li></ol>

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