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You use the key category to define whether the internal table defined by the table type can contain only records with a unique key, or whether the key can have duplicates.

You can define the following key categories:

  • Unique:

    This table type can contain only records with a unique key.

  • Non-Unique:

    A table with this table type can also contain records that do not have different keys for the table type.

  • Not specified:

    The key category is unique or non-unique. This defines a generic table type .


    Only certain combinations of access mode and key category are allowed. These are listed in the following table.

Access Mode

Key category

Not Specified

Not specified

Index Table

Not specified

Standard Table


Sorted Table

Unique, Non-Unique or Not specified

Hashed Table


If the primary key of a standard table or hash table is not specified, you have to select key category Not specified.