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How to identify composite primary key in any MySQL database table?
You can use aggregate function count(*). If it returns a value greater than 1, that would mean the table has composite primary key.
Let us first create a table −
mysql> create table DemoTable1324 -> ( -> StudentId int, -> StudentName varchar(20), -> StudentAge int, -> StudentCountryName varchar(20) -> ); Query OK, 0 rows affected (0.52 sec)
Here is the query to add composite primary key −
mysql> alter table DemoTable1324 ADD CONSTRAINT constr_IdAgeCountry PRIMARY KEY (StudentId, StudentAge,StudentCountryName); Query OK, 0 rows affected (1.29 sec) Records: 0 Duplicates: 0 Warnings: 0
Following is the query to identify composite primary key in any MySQL database table −
mysql> select count(*) AS Total -> from information_schema.KEY_COLUMN_USAGE -> where table_name='DemoTable1324' and table_schema=database();
This will produce the following output −
+-------+ | Total | +-------+ | 3 | +-------+ 1 row in set, 2 warnings (0.76 sec)
Updated on: 05-Nov-2019
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