How do I determine if a column is in the primary key of its table? (SQL Server)

Question

I am currently using...

select Table_Name, Column_name, data_type, is_Nullable
from information_Schema.Columns

...to determine information about columns in a given database for the purposes of generating a DataAccess Layer.

From where can I retrieve information about if these columns are participants in the primary key of their table?

Answer 1

Here is one way (replace 'keycol' with the column name you are searching for):

SELECT K.TABLE_NAME,
K.COLUMN_NAME,
K.CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS C
JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS K
ON C.TABLE_NAME = K.TABLE_NAME
AND C.CONSTRAINT_CATALOG = K.CONSTRAINT_CATALOG
AND C.CONSTRAINT_SCHEMA = K.CONSTRAINT_SCHEMA
AND C.CONSTRAINT_NAME = K.CONSTRAINT_NAME
WHERE C.CONSTRAINT_TYPE = 'PRIMARY KEY'
AND K.COLUMN_NAME = 'keycol';

Answer 2

Similarly, the following will give you information about all the tables and their keys, instead of information about specific columns. This way, you make sure you have all the columns of interest and know what they participate in. In order to see all keys (primary, foreign, unique), comment the WHERE clause.

SELECT K.TABLE_NAME, C.CONSTRAINT_TYPE, K.COLUMN_NAME, K.CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS C
JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS K
ON C.TABLE_NAME = K.TABLE_NAME
AND C.CONSTRAINT_CATALOG = K.CONSTRAINT_CATALOG
AND C.CONSTRAINT_SCHEMA = K.CONSTRAINT_SCHEMA
AND C.CONSTRAINT_NAME = K.CONSTRAINT_NAME
WHERE C.CONSTRAINT_TYPE = 'PRIMARY KEY'
ORDER BY K.TABLE_NAME, C.CONSTRAINT_TYPE, K.CONSTRAINT_NAME