Rule Definition
As the FOR ALL ENTRIES IN is part of the WHERE clause, an empty internal table can end-up in a full table scan and thus cause performance troubles. This is why it is mandatory to include an emptiness check before any use of the FOR ALL ENTRIES IN statement.

Remediation
Use an emptiness check based on one of the following syntax : CHECK NOT ts_table[] IS INITIAL. or IF NOT ts_table[] IS INITIAL.

Violation Code Sample

* Select orders for specific material and order type
SELECT matnr auart vbeln posnr
              FROM vapma
              INTO TABLE ts_vapma[]
              WHERE matnr IN so_matnr
             AND auart IN so_auart.

* Use this result to read the detail data from VBAP: 
* Order Item Data
SELECT matnr vbeln kwmeng vrkme
              FROM vbap
              INTO TABLE ts_orders
              FOR ALL ENTRIES IN ts_vapma[]
              WHERE vbeln = ts_vapma
              AND posnr = ts_vapma-posnr

Fixed Code Sample

* Select orders for specific material and order type
SELECT matnr auart vbeln posnr
              FROM vapma
              INTO TABLE ts_vapma[]
              WHERE matnr IN so_matnr
              AND auart IN so_auart.

* Use this result to read the detail data from VBAP: 
* Order Item Data
IF NOT ts_vapma[] IS INITIAL.
SELECT matnr vbeln kwmeng vrkme
              FROM vbap
              INTO TABLE ts_orders
              FOR ALL ENTRIES IN ts_vapma[]
              WHERE vbeln = ts_vapma
              AND posnr = ts_vapma-posnr.
ENDIF.

Enhancing the Quality of ABAP Development, Meijs-Krouwels-Heulmans-Sommen, SAP Press ISBN 1-59229-030-2