Try this:

.... where not empty(taba.field2) AND NOT ISNULL(taba.field2)

>I have executed the following SQL command both in VFP8 and VFP9 and the results were different.
>
>select * from tabb left join taba on left(tabb.id,4)=taba.id where not empty(taba.field2)
>
>where taba is:
>
>id field1 field2
>0101 desc 1
>0201 desc 2 X
>
>and tabb is:
>
>id field1
>010101 1
>010102 2
>010103 3
>020101 1
>020102 2
>020103 3
>
>the result (which i think is the correct) in VFP8 is:
>
>id_a field1_a id_b field1_b field2
>020101 1 0201 desc 2 X
>020102 2 0201 desc 2 X
>020103 3 0201 desc 2 X
>
>and the result in VFP9 is:
>
>id_a field1_a id_b field1_b field2
>010101 1 .null. .null. .null.
>010102 2 .null. .null. .null.
>010103 3 .null. .null. .null.
>020101 1 0201 desc 2 X
>020102 2 0201 desc 2 X
>020103 3 0201 desc 2 X
>
>I haven´t read anything in the documentation about different behavior in the SQL command that could cause this.
>
>If someone have a clue, please tell me.
>
>Thnk you.