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MySQL: Determine Table’s Primary Key Dynamically

Solution:1

SHOW INDEX FROM <tablename>

You want the row where Key_name = PRIMARY

http://dev.mysql.com/doc/refman/5.0/en/show-index.html

You’ll probably want to cache the results — it takes a while to run SHOW statements on all the tables you might need to work with.

Solution:2

It might be not advised but works just fine:

SHOW INDEX FROM <table_name> WHERE Key_name = 'PRIMARY';

The solid way is to use information_schema:

SELECT k.COLUMN_NAME
FROM information_schema.table_constraints t
LEFT JOIN information_schema.key_column_usage k
USING(constraint_name,table_schema,table_name)
WHERE t.constraint_type='PRIMARY KEY'
    AND t.table_schema=DATABASE()
    AND t.table_name='owalog';

As presented on the mysql-list. However its a few times slower from the first solution.