A9xx sounds like generated price condition table.
First selecting more than required then deleting from the result is almost always a bad idea.
This might well lead to your problem here.
Why did you not include the condition for DATAB in the WHERE-condition?
What is the primary key fields of this table?
Is there any secondary index created for this table, if yes, for which fields?
What is the content of range SMATNR at runtime?
Do you really need all columns from A957 for further processing?
What are you doing with the selected data from A957?
Please try answering all questions.
Thomas