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Data Type of an Internal Table

A table type defined in ABAP Dictionary or using TYPES or DATA is specified fully using:

Unlike all other data types, a table type defined in ABAP Dictionary or using TYPES does not have to be specified in full. You can omit either only the keys or the row type and the keys from the definition. This makes the type generic and it can be used only for typings of field symbols and formal parameters. You can use the predefined generic ABAP types ANY TABLE and INDEX TABLE for these purposes. The first type includes all table categories, the second type includes standard tables and sorted tables, known as index tables.

Like strings, internal tables are dynamic data objects. Their row type, table category, and table key are always specified in full, but the number of rows is variable and restricted only by the capacity of the system installation (see Maximum Size of Dynamic Data Objects).