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Key Definition (key_definition) 

A key definition in a CREATE TABLE statement or an ALTER TABLE statement defines the key of a base table. The key definition is introduced by the keywords PRIMARY KEY.

Syntax

<key_definition> :: PRIMARY KEY (<column_name>,...)

column_name

SQL statement for creating a person table with a one-column primary key for the column cno:

CREATE TABLE person (cno FIXED(4), firstname CHAR(7), name CHAR(7), account FIXED(7,2), PRIMARY KEY (cno))

Rows are inserted in the same way as in a base table without a key definition. Double entries for the customer number, however, are rejected.

Explanation

The column name must identify a column in the base table. The specified column names are key columns in the table.

A key column must not identify a column of the data type LONG and is always a NOT NULL column. The database system ensures that no key column has a NULL value and that no two rows of the table have the same values in all key columns.

See also:

Technical Specifications

 

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