SAP LOGEXP ASSIGNED

Get Example source ABAP code based on a different SAP table
  SAP Help

ARTICLE
• IS ASSIGNED ABAP_RELAT_EXPR
• IS NOT ASSIGNED ABAP_RELAT_EXPR

rel_exp - IS ASSIGNED

Syntax
ABAP_KEY ... <(><<)>fs> IS [NOT] ASSIGNED ...

Effect
This predicate expression checks whether a memory area is assigned to a field symbol <(><<)>fs>. The expression is true if the field symbol points to a memory area. <(><<)>fs> expects a field symbol declared using FIELD-SYMBOLS or declared inline using FIELD-SYMBOL( ).
If the addition NOT is used, the expression is true if no memory area is assigned to the field symbol.

Example
Assigns a data object to a field symbol if no memory area has been assigned yet. FIELD-SYMBOLS <(><<)>fs> TYPE c.

...

IF <(><<)>fs> IS NOT ASSIGNED.
ASSIGN 'Standard Text' TO <(><<)>fs>.
ENDIF.

...