SQL query to find Primary Key of a table?

Try this query in SQL server:

SELECT     X.NAME AS INDEXNAME,
           COL_NAME(IC.OBJECT_ID,IC.COLUMN_ID) AS COLUMNNAME
FROM       SYS.INDEXES  X 
INNER JOIN SYS.INDEX_COLUMNS  IC 
        ON X.OBJECT_ID = IC.OBJECT_ID
       AND X.INDEX_ID = IC.INDEX_ID
WHERE      X.IS_PRIMARY_KEY = 1
  AND      OBJECT_NAME(IC.OBJECT_ID)='YOUR_TABLE'

This is a duplicate question:

credit to Lukmdo for this answer:

It might be not advised but works just fine:

show index from TABLE 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';

For Oracle, you can look it up in the ALL_CONSTRAINTS table:

SELECT a.COLUMN_NAME
FROM all_cons_columns a INNER JOIN all_constraints c 
     ON a.constraint_name = c.constraint_name 
WHERE c.table_name = 'TBL'
  AND c.constraint_type = 'P';

DEMO.

For SQL Server, it was already answered here, and for MySQL check @ajon's answer.

For MySQL:

SELECT GROUP_CONCAT(COLUMN_NAME), TABLE_NAME
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE
  TABLE_SCHEMA = '**database name**'
  AND CONSTRAINT_NAME='PRIMARY'
GROUP BY TABLE_NAME;

Warning a primary key with two columns will have them separated by a coma (,)