On Transact SQL language the sp_helpconstraint is part of Database Engine Stored Procedures.
Returns information like constraint types, constraint names, the columns on which they have been defined, status, and the expression that defines the constraint.
sp_helpconstraint [ @objectname = ] 'table'
[ , [ @nomsg = ] 'no_message' ]
EXEC sp_helpconstraint 'Customers';