SQL Server/T-SQL Tutorial/System Tables Views/sysconstraints

The system table sysconstraints contains one row for every integrity constraint that is defined for a database object using the CREATE TABLE or ALTER TABLE statement.

status  The type of the integrity constraint: 1 = PRIMARY KEY constraint; 2 = UNIQUE KEY constraint; 3 = FOREIGN KEY constraint; 4 = CHECK constraint; 5 = DEFAULT constraint; 16 = column-level constraint; 32 = table-level constraint
7>
8>
9> select  top 10 * from sysconstraints;
10> GO
constid     id          colid  spare1 status      actions     error
----------- ----------- ------ ------ ----------- ----------- -----------
 1131151075  1115151018      6      0      133141        4096           0
(1 rows affected)