Inner join searches too many entries

Hi experts,

In a user exit following code is used:

DATA : h_rsnum LIKE afko-rsnum,

h_charg LIKE resb-charg,

h_matnr LIKE resb-matnr,

SELECT SINGLE rsnum INTO h_rsnum

FROM afko

WHERE aufnr = x_bncom-aufnr.

IF sy-subrc = 0 .

SELECT resb_{charg resb}matnr

INTO (h_charg, h_matnr)

FROM mara INNER JOIN resb

ON mara_{matnr = resb}matnr

WHERE resb~rsnum = h_rsnum

AND resb~charg NE space

AND mara_{mtart = 'HALB' OR mara}mtart = 'FERT'.

ENDSELECT.

Goal of the source code is to detemine the reservation number of a process order. From table RESB with key h_rsnum, the material nb and the batch nb of the single material with material type HALB or FERT needs to be selected.

During debugging I found out that this code searches into a very long list of materials before ending up with the correct h_charg and h_matnr.

If the condition resb~rsnum = h_rsnum would be taken into account when creating the inner join, the list would only contain 20 materials maximum.

Can this behaviour be changed and how to do it?

Rgds,

Suzy