Places a constraint on the given relation.
Further calls to functions like dbplus_curr() or dbplus_next() will only return tuples matching the given constraints.
relationA relation opened by dbplus_open().
constraints
Constraints are triplets of strings containing of a domain name,
a comparison operator and a comparison value. The
constraints parameter array may consist of
a collection of string arrays, each of which contains a domain, an
operator and a value, or of a single string array containing a
multiple of three elements.
The comparison operator may be one of the following strings: '==', '>', '>=', '<', '<=', '!=', '~' for a regular expression match and 'BAND' or 'BOR' for bitwise operations.
tuple