Places a constraint on the given relation.
A relation opened by dbplus_open().
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.
This function is EXPERIMENTAL. The behaviour of this function, the name of this function, and anything else documented about this function may change without notice in a future release of PHP. Use this function at your own risk.