SAP STANDARD KEY GLOSRY documentation, setup help and example usage

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standard key
Primary table key of an internal table , whose key fields in a structured row type are all table fields with character-like data types and byte-like data types . If the row type contains substructures , these are broken down into elementary components . The standard key for non-structured row types is the entire table row if the row type itself is not a table type. If there are no corresponding table fields, or the row type itself is a table type, the standard key from standard tables is empty or contains no key fields.
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