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Wednesday, May 23, 2007

Sample Code for Using Field-Groups

A Note on the Use of Field Groups...Because field-groups write their data to paging space (rather than storing it in memory), they are appropriate only for processing lists with lots (like 50,000 or more) of records. If you expect your programs to be handling tens of thousands of records, you should:
analyze the expected size of your lists. For instance, if your system has 512M of main memory, you may decide that you don't want any report to use more than 15M of memory for its lists. In that program, you may have a list:


begin of mylist occurs XXX,
dat1(100) type c,
dat2(50) type c,
dat3(10) type c,
end of list. Then each record takes up approximately 160 bytes; so every 6 records take up approximately 1K. For this list structure, it would take about 90,000 records to use up 15M RAM.
decide the maximum amount of memory you want your program to use
decide whether to use field-groups or something else (like internal tables). If you expect the size of your list to be greater than the amount of memory you want your program to use, then use field-groups (actually, if you use internal tables, and the number of records exceeds the number of records in your OCCURS statement, the system just writes those extra records to the paging space. So is there really any difference between just using an internal table with an OCCURS 0 statement-- which would write the entire table to paging space-- and using field-groups? According to Gareth M. de Bruyn and Robert Lyfareff in Introduction to ABAP/4 Programming for SAP, field-groups are stored more efficiently, and have better performance. They recommend field-groups for lists of 100,000 or more records).
document.write (RepName);

Field-Groups Sample Code
*&---------------------------------------------------------------------*
*& Report ZSPFLI *
*& *
*&---------------------------------------------------------------------*
REPORT ZSPFLI LINE-SIZE 132 LINE-COUNT 65(3)
NO STANDARD PAGE HEADING.
TABLES:SPFLI,SCARR, SFLIGHT, SBOOK.
SELECT-OPTIONS: MYCARRID FOR SPFLI-CARRID.
FIELD-GROUPS: HEADER, SPFLI_FG, SFLIGHT_FG, SBOOK_FG.
INSERT:
SPFLI-CARRID
SPFLI-CONNID
SFLIGHT-FLDATE
SBOOK-BOOKID
INTO HEADER,
SPFLI-CARRID
SPFLI-CONNID
SPFLI-CITYFROM
SPFLI-AIRPFROM
SPFLI-CITYTO
SPFLI-AIRPTO
SPFLI-DEPTIME
SCARR-CARRNAME
INTO SPFLI_FG,
SFLIGHT-FLDATE
SFLIGHT-SEATSMAX
SFLIGHT-SEATSOCC
SFLIGHT-PRICE
INTO SFLIGHT_FG,
SBOOK-BOOKID
SBOOK-CUSTOMID
SBOOK-CUSTTYPE
SBOOK-SMOKER
INTO SBOOK_FG.
SELECT * FROM SPFLI WHERE CARRID IN MYCARRID.
SELECT SINGLE * FROM SCARR WHERE CARRID = SPFLI-CARRID.
EXTRACT SPFLI_FG.
SELECT * FROM SFLIGHT
WHERE CARRID = SPFLI-CARRID AND CONNID = SPFLI-CONNID.
EXTRACT SFLIGHT_FG.
SELECT * FROM SBOOK
WHERE CARRID = SFLIGHT-CARRID AND
CONNID = SFLIGHT-CONNID AND FLDATE = SFLIGHT-FLDATE.
EXTRACT SBOOK_FG.
CLEAR SBOOK.
ENDSELECT.
CLEAR SFLIGHT.
ENDSELECT.
CLEAR SPFLI.
ENDSELECT.
SORT.
LOOP.
AT SPFLI_FG.
FORMAT COLOR COL_HEADING.
WRITE: / SCARR-CARRNAME,
SPFLI-CONNID, SPFLI-CITYFROM,
SPFLI-AIRPFROM, SPFLI-CITYTO, SPFLI-AIRPTO, SPFLI-DEPTIME.
FORMAT COLOR OFF.
ENDAT.
AT SFLIGHT_FG.
WRITE: /15 SFLIGHT-FLDATE, SFLIGHT-PRICE, SFLIGHT-SEATSMAX,
SFLIGHT-SEATSOCC.
ENDAT.
AT SBOOK_FG.
WRITE: /30 SBOOK-BOOKID, SBOOK-CUSTOMID,
SBOOK-CUSTTYPE, SBOOK-SMOKER.
ENDAT.
ENDLOOP.
*&---------------------------------------------------------------------*
*& END OF REPORT *
*&---------------------------------------------------------------------*

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