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AT - Control Level Processing

Short Reference

Other versions: 7.31 | 7.40 | 7.54

Syntax


LOOP AT itab result
[cond]. 
  [AT FIRST. 

     ... 
   ENDAT.] 

    [AT NEW comp1. 

       ... 
     ENDAT. 

       [AT NEW comp2. 

         ... 
       ENDAT. 

         [...]]] 
           [ ... ] 

       [[[...] 
 
     AT END OF comp2. 

         ... 
       ENDAT.] 

     AT END OF comp1. 

       ... 
     ENDAT.] 

  [AT LAST. 
     ... 
  ENDAT.] 
ENDLOOP.

Extras

1. ...  FIRST

2. ... {NEW}|{END OF} compi

3. ...  LAST

Effect

The statement block of a LOOP without the addition GROUP BY can contain control structures for control level processing. The corresponding control statement is AT. The statements AT and ENDAT define statement blocks that are executed at control breaks, meaning in the transition of a control level to another control level. The additions of the statements AT define the criteria for a control break and hence the control levels. Control breaks between control levels are a result of the row structure and the processing order in which the LOOP reads the rows of the internal table. Within the statement blocks, the statement SUM can be specified to total the numeric components of a control level.

Apart from the special variants AT FIRST and AT LAST, control levels are defined using the variant AT NEW and the sequence of rows in the internal table. These are the rows that have the same content in a control key defined in their initial parts. It is possible, from a syntax point of view, to arrange AT control structures in any order and to nest them, however effective control level processing is usually only achieved by the arrangement above. Here, the control structures are specified in accordance with the arrangement of the components in the control key and are not nested.

The statement blocks within the AT-ENDAT control structures are executed if an appropriate control break is made in the current table row. Statements in the LOOP-ENDLOOP control structure that are not executed within an AT-ENDAT control structure are executed in each pass of the loop. The following rules must be followed for effective control level processing:

  • A table key specified in LOOP in cond must be chosen so that it produces the required processing order of the imported rows.
  • A restricting condition specified in LOOP in cond must select a contiguous row block in the internal table.
  • The internal table cannot be modified within the LOOP loop.
  • A work area wa specified in the LOOP statement after the addition INTO must be compatible with the row type of the table.
  • A field symbol <fs> specified in the statement LOOP after the addition ASSIGNING must be typed with the row type of the table.
  • The content of a work area wa specified in the statement LOOP after the addition INTO cannot be modified.

If the addition INTO is used in the statement LOOP to assign the content of the current row to a work area wa, its content is modified as follows when the AT-ENDAT control structure is entered:

  • The components of the current control key remain unchanged.
  • All components with a character-like flat data type to the right of the current control key are set to character "*" in every position.
  • All the other components to the right of the current control key are set to their initial value.

When the AT-ENDAT control structure is exited, the content of the current table row is assigned to the entire work area wa.


Notes

  • When the additions ASSIGNING and REFERENCE INTO are used, the referenced table rows are not modified when entering and exiting the AT-ENDAT control structure.
  • If INTO is used, note that " character-like" has a different definition in Unicode programs and obsolete non-Unicode programs, which means that identical structures can produce different results.
  • Control level processing with the statement AT is not possible in LOOPs across row groups with the addition GROUP BY, including member loops using LOOP AT GROUP.
  • A common case is when the internal table is sorted exactly by the order of the components of its row type, by the first component first, then the second component, and so on. In this case, control level processing can also be expressed using a grouping with the addition GROUP BY.
  • If possible, the use of the addition GROUP BY is recommended, since the grouping is not determined by the structure of the rows and the processing order in this case.


Example

See Examples of Control Level Processing.

Addition 1

...  FIRST

Effect

The control level is defined by the first row of the internal table. The control break takes place when this row is read.


Note

In the control level AT FIRST, the current control key does not contain any components and all character-like components of the work area wa are filled with "*" and all remaining components are set to their initial value.

Addition 2

... {NEW}|{END OF} compi

Effect

Control levels are defined by the beginning or end of a group of rows with the same content in the component compi (where i = 1, 2, and so on) and in the components to the left of compi. The content of these components determines the control key. The control breaks take place when the content of the component compi or another component to the left of compi changes.

The compi components can be specified as described in Specification of Components, with the limitation that access to data objects using references is not possible here. The following is therefore not possible:

  • Specifying data objects using data references
  • Specifying attributes of objects using object references

Otherwise, the specified components can have any data type. The relevant comparison rules apply to the evaluation.


Notes

  • In this case, control levels consist of the contiguous rows of the internal table that have the same content in an initial part.
  • An obsolete variant allows field symbols to also be specified, outside of classes compi.

Addition 3

...  LAST

Effect

The control level is defined by the last row of the internal table. The control break takes place when this row is read.


Note

In the control level AT LAST, the current control key does not contain any components and all character-like components of the work area wa are filled with "*" and all remaining components are set to their initial value.

Exceptions


Non-Catchable Exceptions

  • Cause: Invalid substring access when the control break criterion is specified dynamically.
    Runtime Error: AT_BAD_PARTIAL_FIELD_ACCESS
  • Cause: The control break criterion is specified dynamically using the field symbol and the field symbol does not point to the LOOP output area.
    Runtime Error: AT_ITAB_FIELD_INVALID
  • Cause: The control break criterion is specified dynamically using (name) and the name field does not contain a valid substring name.
    Runtime Error: ITAB_ILLEGAL_COMPONENT
  • Cause: Overflow of totals with SUM.
    Runtime Error: SUM_OVERFLOW

Continue

SUM

ENDAT

Examples of Control Level Processing