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LOOP AT itab - GROUP BY

Short Reference

Other versions: 7.31 | 7.40 | 7.54

Syntax


LOOP AT itab result
[cond] GROUP BY group_key 

                           [ASCENDING|DESCENDING [AS TEXT]] 

                           [WITHOUT MEMBERS] 

                 
         [group_result]. 

  ... 
  [LOOP AT GROUP ... 

    ... 
  ENDLOOP.] 
  ... 
ENDLOOP.

Extras

1. ... ASCENDING|DESCENDING [AS TEXT]

2. ... WITHOUT MEMBERS

Effect

This variant of the statement LOOP AT itab groups the rows of the internal table and executes a loop across the groups. The same applies to the syntax of the additions result and cond as to a loop across rows with the exception that the addition TRANSPORTING NO FIELDS cannot be specified.

If the addition GROUP BY is specified, the LOOP is processed in two phases:

  • Grouping

    In the first phase, all rows specified by the conditions cond are read in the processing order specified in a loop across rows. The statements in the statement block between LOOP and ENDLOOP are not executed during this operation. For each row read, a group key is constructed in the group key expression group_key instead. Each group key represents a group. Each row is assigned to precisely one group (as a member). This is the group of all rows with the same group key. If the addition WITHOUT MEMBERS is not used, this assignment is internal and can be used for access to the members of a group in the second phase.
  • Group Loop

    In the second phase, a loop is executed across all groups. The statements in the statement block between LOOP and ENDLOOP are executed for each loop pass. The output behavior for the group loop is defined in group_result and the corresponding values can be accessed in the loop. If the assignment of the table rows to their groups is defined, a member loop LOOP AT GROUP can be nested in the LOOP to read the rows in each group.

The default order of the groups in the group loop plus the order of the members within a group is defined by the processing order of the LOOP in the first phase:

  • The default order of the groups is based on the time their group key is first created, which itself can be overridden using the additions ASCENDING or DESCENDING.
  • If the assignment of the rows to their group is defined, the order of the rows of a group is based on the time they are assigned to the group. This defines, in particular, the first row of each group, used as a representative in the representative binding.

The internal table itab cannot be modified in the group loop unless the addition WITHOUT MEMBERS is specified.

System Fields

This variant of the statement LOOP AT with the addition GROUP BY sets the values of the system field sy-tabix in the group loop as follows:

  • If a representative binding is defined in the output behavior, sy-tabix is set to the value that would be set for the row representing the group in the LOOP without grouping.
  • If a group key binding is defined in the output behavior, the groups are counted in sy-tabix. The first loop pass sets sy-tabix to 1 and each subsequent loop pass raises it by 1.

The same applies to sy-subrc as in a loop across rows.


Notes

  • A grouping (the assignment of rows to a group) exists only within the group loop and a group can only be addressed here after LOOP AT GROUP or FOR ... IN GROUP.
  • A LOOP with the addition GROUP BY is not possible for mesh paths.
  • No control level processing with the statement AT is possible in a LOOP with the addition GROUP BY.
  • Unlike in control level processing, a grouping with GROUP BY is not defined by the structure of the rows and the processing order of the loop. A grouping with GROUP BY can usually replace control level processing in cases where the internal table is sorted before the loop by the group key (see the example).
  • Internal tables can also be group using the expression FOR GROUPS ... OF.

Addition 1

... ASCENDING|DESCENDING [AS TEXT]

Effect

These additions sort the groups by the group key in ascending or descending order before the group loop is executed. The groups are sorted in exactly the same way as when the statement SORT is used on an internal table whose primary table key is the group key and the addition AS TEXT is applied accordingly.

The group loop is executed in the sort order. If the additions ASCENDING and DESCENDING are not specified, the groups are in the order in which the value of a group key was constructed for the first time.

Addition 2

... WITHOUT MEMBERS

Effect

The addition WITHOUT MEMBERS deactivates the default internal variant of the assignment of each table row to its group. This addition constructs groups but there is not access to the rows of the groups in the group loop. If the addition WITHOUT MEMBERS is specified,

  • the output behavior cannot be defined for a row of the group as a representative, a group key binding must be defined,
  • the group loop cannot contain a nested member loop LOOP AT GROUP,
  • the internal table itab cannot be modified in the group loop.


Note

The addition WITHOUT MEMBERS is used to improve performance in all cases where the content of the groups is not required.


Example

See the examples for grouping internal tables.

Continue

LOOP AT itab - group_key

LOOP AT itab - group_result

LOOP AT GROUP

Examples of Grouping with LOOP