ABAP DATA PRIMARY KEY Statement syntax and functionality in SAP

DATA - key

Short Reference

ABAP Syntax ... { [UNIQUE | NON-UNIQUE]
{ {KEY [primary_key [ALIAS key_name] COMPONENTS] comp1 comp2 ...}
| {DEFAULT KEY} }}
| { EMPTY KEY } ... .

ABAP_ALTERNATIVES:
1 ... [UNIQUE|NON-UNIQUE] {KEY ...}|{DEFAULT KEY}
2 ... EMPTY KEY

ABAP_ALTERNATIVE_1 ... [UNIQUE|NON-UNIQUE] {KEY ...}|{DEFAULT KEY}

What does it do? Defines the primary table key of an internal table by specifying components or as a standard key. The syntax and semantics of the additions are the same as for the
TYPES statement for dedicated table types, with the difference that the primary key of a bound table type must always be specified completely:
For standard tables only the
NON-UNIQUE KEY addition can be specified. If uniqueness is not specified, this is added implicitly. The addition UNIQUE KEY cannot be specified.

For sorted tables , one of the two additions UNIQUE KEY or NON-UNIQUE KEY must be specified.

For hashed tables , the UNIQUE KEY
addition must be specified.

If no primary key is specified for DATA using WITH , the addition WITH NON-UNIQUE DEFAULT KEY is added implicitly for standard tables. This gives the table a
standard key , which can be empty. In sorted tables and hashed tables, the primary key must be specified explicitly and cannot be empty.
If the name of the primary key primary_key is specified explicitly, the WITH HEADER LINE addition can no longer be specified, even outside the classes.

Latest notes: The declaration of the primary table key as a standard key can be critical for various reasons. It is best to specify key fields explicitly instead. In particular, make sure that the declaration of the standard key is not added by mistake because the key has not been specified explicitly.

ABAP_ALTERNATIVE_2 ... EMPTY KEY

What does it do? Defines an empty primary key in an internal table. This variant is possible for standard tables only. The syntax and semantics are the same as for the statement TYPES .
Latest notes: The addition EMPTY KEY can clarify situations where the definition of a table key is not important.
We generally recommend EMPTY KEY instead of not specifying a key definition, since otherwise the standard key is used, which can often lead to unexpected results.

ABAP DATA PRIMARY KEY Statement syntax, information and example SAP source code