INDEX_FLAG is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "Structure with index field and any indicator" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_INDEX_FLAG TYPE INDEX_FLAG.
The INDEX_FLAG table consists of various fields, each holding specific information or linking keys about Structure with index field and any indicator data available in SAP. These include FLAG_MAT (Single-Character Indicator), FLAG_PRT (Single-Character Indicator), FLAG_SOP (Single-Character Indicator), FLAG_PST (Single-Character Indicator)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .