performance tuning

will the following code reduce the performance?

LOOP AT ITAB.

CLEAR : ITAB-ERDAT, ITAB-VBELN, ITAB-LIFNR.

SELECT SINGLE ERDAT VBELN

INTO (ITAB-ERDAT, ITAB-VBELN)

FROM VBFA

WHERE VBELV = ITAB-BELNR

AND ( VBTYP_N = 'U' OR BWART = '641' ) .

IF SY-SUBRC EQ 0.

SELECT SINGLE LIFNR

INTO ITAB-LIFNR

FROM VBPA

WHERE VBELN = ITAB-VBELN

AND PARVW = 'SP'.

ENDIF.

MODIFY ITAB TRANSPORTING ERDAT VBELN LIFNR.

ENDLOOP.