Add Primary Key to Existing Table SQL

Code to add a primary key to existing table SQL.

ALTER TABLE table_name ADD PRIMARY KEY ( the_id, the_name, PMID );

Syntax.

ALTER TABLE <Table_Name> DROP CONSTRAINT <constraint_name>;

ALTER TABLE <Table_Name> ADD CONSTRAINT <constraint_name> PRIMARY KEY ( <Column1>, <Column2> )

Live example.

ALTER TABLE table_name ADD PRIMARY KEY ( id );

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