Determining the Primary Key of a table without knowing it’s name

So, I’ve been trying to find more technical fodder for blog posts lately in order to get in the habit of blogging on a regular basis, so I thought I would explore a few of my higher-ranked answers on StackOverflow and provide a little more detail than that site provides.  This is my highest-rated answer (sad, I know, compared to some posters on the site):

Determine a table’s primary key using TSQL

I’d like to determine the primary key of a table using TSQL (stored procedure or system table is fine). Is there such a mechanism in SQL Server (2005 or 2008)?

My answer:

This should get you started:

SELECT *
    FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc
        JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE ccu ON tc.CONSTRAINT_NAME = ccu.Constraint_name
    WHERE tc.CONSTRAINT_TYPE = 'Primary Key'

 

Besides the obvious faux pas of using SELECT * in a query, you’ll note that I used the INFORMATION_SCHEMA views; I try to use these views wherever possible because of the portability factor.  In theory, I should be able to apply this exact same query to a MySQL or Oracle database, and get similar results from the system schema.

The added benefit of this query is that it allows you to discover other things about your PRIMARY KEYs, like looking for system named keys:

SELECT  tc.TABLE_CATALOG, tc.TABLE_SCHEMA, tc.TABLE_NAME, ccu.CONSTRAINT_NAME, ccu.COLUMN_NAME
FROM    INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc
        JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE ccu ON tc.CONSTRAINT_NAME = ccu.Constraint_name
WHERE   tc.CONSTRAINT_TYPE = 'Primary Key'
    AND ccu.CONSTRAINT_NAME LIKE 'PK%/_/_%' ESCAPE '/'

or finding PRIMARY KEYs which have more than one column defined:

SELECT  tc.TABLE_CATALOG, tc.TABLE_SCHEMA, tc.TABLE_NAME, ccu.CONSTRAINT_NAME
FROM    INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc
        JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE ccu ON tc.CONSTRAINT_NAME = ccu.Constraint_name
WHERE   tc.CONSTRAINT_TYPE = 'Primary Key'
GROUP BY tc.TABLE_CATALOG, tc.TABLE_SCHEMA, tc.TABLE_NAME, ccu.CONSTRAINT_NAME
HAVING COUNT(*) > 1

July 23, 2014 · stuart · No Comments
Tags: , , ,  · Posted in: SQL, SQL Server, SQLServerPedia Syndication

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