INFORMATION_SCHEMA primary key

The recommended way to retrieve information about your database, tables or columns is to use the INFORMATION_SCHEMA views. These views were introduced in the SQL-92 standard, and all database vendors have adopted or will soon adopt this standard.

Retrieving information about primary keys may require joining a couple of these views. For example, the following query (posted here and found via a Web search for "information_schema primary key") will show the primary keys for each table --

SELECT
 T.TABLE_NAME,
 COALESCE( CU.CONSTRAINT_NAME , '(no primary key)') 
    AS PRIMARY_KEY_NAME,
 CU.COLUMN_NAME 
FROM INFORMATION_SCHEMA.TABLES AS T
LEFT JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS TC
 ON TC.TABLE_CATALOG = T.TABLE_CATALOG
 AND TC.TABLE_SCHEMA = T.TABLE_SCHEMA
 AND TC.TABLE_NAME = T.TABLE_NAME
 AND TC.CONSTRAINT_TYPE = 'PRIMARY KEY'
LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS CU
 ON CU.CONSTRAINT_CATALOG = TC.CONSTRAINT_CATALOG
 AND CU.CONSTRAINT_SCHEMA = TC.CONSTRAINT_SCHEMA
 AND CU.CONSTRAINT_NAME = TC.CONSTRAINT_NAME
WHERE
 T.TABLE_TYPE = 'BASE TABLE'
ORDER BY
 T.TABLE_NAME,
 CU.ORDINAL_POSITION

Note that this query works in Microsoft SQL Server but might need tweaking for whatever database system you're using.