Returns the schema of a database file as an associated array. The key name is equal to the field name. If mode is PX_KEYTOLOWER or PX_KEYTOUPPER the key will be converted to lower or upper case. If mode is 0 or not passed at all, then the key name will be identical to the field name. Each array element is itself an associated array containing the two fields 'type' and 'size'. 'type' is one of the constants in table Constants for field types.