SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE OBJECTPROPERTY(OBJECT_ID(CONSTRAINT_NAME), 'IsPrimaryKey') = 1
AND TABLE_NAME = 'tablename';
SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE OBJECTPROPERTY(OBJECT_ID(CONSTRAINT_NAME), 'IsPrimaryKey') = 1
AND TABLE_NAME = 'tablename';