PostgreSQL boolean expressions return "t" for true and "f" for false.
MySQL:
> var_dump(wfGetDB(DB_PRIMARY)->selectRow('',['false' => '1=0', 'true' => '1=1'],''));
object(stdClass)#982 (2) {
["false"]=>
string(1) "0"
["true"]=>
string(1) "1"
}SQLite:
> var_dump(wfGetDB(DB_PRIMARY)->selectRow('',['false' => '1=0', 'true' => '1=1'],''));
object(stdClass)#353 (2) {
["false"]=>
string(1) "0"
["true"]=>
string(1) "1"
}PostgreSQL:
> var_dump(wfGetDB(DB_PRIMARY)->selectRow('',['false' => '1=0', 'true' => '1=1'],''));
object(stdClass)#348 (2) {
["false"]=>
string(1) "f"
["true"]=>
string(1) "t"
}PostgreSQL alone returns a value which is not falsey in PHP. I believe this can and should be hacked around in PostgresResultWrapper. There is pg_field_type().