A599 is a standard SAP Table which is used to store SD doc./Item/Variant data in SAP systems, such as SAP R/3, S/4HANA, depending on the version and release level.
The A599 table consists of various fields, each holding specific information or linking keys about SD doc./Item/Variant data available in SAP. These include KAPPL (Application), KSCHL (Condition type), VBELN (Sales and Distribution Document Number), POSNR (Item number of the SD document)... 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. .