A field group combines several fields under one name. For clarity, you should declare your field groups at the end of the declaration part of your program.
A field group does not reserve storage space for the fields, but contains pointers to existing fields. When filling the extract dataset with records, these pointers determine the contents of the stored records.
Once you have declared the possible record types as field groups and defined their structure, you can fill the extract dataset using the following statements: EXTRACT . When the first EXTRACT statement occurs in a program, the system creates the extract dataset and adds the first extract record to it. In each subsequent EXTRACT statement, the new extract record is added to the dataset EXTRACT HEADER. When you extract the data, the record is filled with the current values of the corresponding fields. As soon as the system has processed the first EXTRACT statement for a field group , the structure of the corresponding extract record in the extract dataset is fixed. You can no longer insert new fields into the field groups and HEADER. If you try to modify one of the field groups afterwards and use it in another EXTRACT statement, a runtime error occurs. By processing EXTRACT statements several times using different field groups, you fill the extract dataset with records of different length and structure. Since you can modify field groups dynamically up to their first usage in an EXTRACT statement, extract datasets provide the advantage that you need not determine the structure at the beginning of the program.
give the logical database name as F1S in the attributes of the program
NODES: spfli, sflight.
FIELD-GROUPS: header, flight_info, flight_date.
INSERT: spfli-carrid spfli-connid sflight-fldate
INTO header,
spfli-cityfrom spfli-cityto
INTO flight_info.
START-OF-SELECTION.
GET spfli.
EXTRACT flight_info.
GET sflight.
EXTRACT flight_date.
end-of-selection.
loop.
write:/ spfli-carrid,spfli-connid,sflight-fldate.
endloop.
Bluesky
