Microsoft KB Archive/168207

= PRB: Cannot Find NULL Records with Parameterized Query =

Article ID: 168207

Article Last Modified on 1/8/2003

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APPLIES TO


 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 6.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition

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This article was previously published under Q168207



SYMPTOMS
Running a parameterized query against a Jet database where the parameter variable is equal to NULL will not return any records. Running a query without the parameter variable that specifically searches for NULL will succeed as expected.



CAUSE
A variable with a NULL value sent in as the parameter is not equal to what the JET engine recognizes as NULL. The values of the NULLs do not match.



RESOLUTION
Before calling the code that executes the query, use an IF statement that checks the value of the parameter. If the value is NULL, run a different query that specifically looks for a NULL value, otherwise run the original, parameterized query.

Example: Dim p1 as long dim r1 as recordset dim SQLstring as string dim p1 as long

if p1 = NULL then SQLstring = "SELECT Table1.Field1 FROM Table1 _       WHERE (((Table1.Field1) Is Null));" 'Looking specifically for a Null else SQLstring = "SELECT Table1.Field1 FROM Table1 _      WHERE (((Table1.Field1)=[" & p1 & "]));" 'Parameterized query end if

set r1 = MyDatabase.openrecordset(SQLstring, dbOpenDynaset)



STATUS
This behavior is by design.



Steps to Reproduce Behavior
 Create a database with one table. Create one field in that table. Put a NULL (empty string) in the first record of the table. Create two querydefs:

 Query1 will search specifically for records that equal NULL. Query2 will be the same as Query1 except that the search criteria is parameterized. </li> Run Query1.</li> Run Query2, setting the parameter variable as NULL.</li></ol>

Results:

Query1 will have one record while Query2 will have no records.

Additional query words: kbVBp500 kbVBp600 kbdse kbDSupport kbVBp kbNoKeyWord

Keywords: kbprb KB168207

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