Re: [GENERAL] hard parse?
| От | David G. Johnston |
|---|---|
| Тема | Re: [GENERAL] hard parse? |
| Дата | |
| Msg-id | CAKFQuwaCCRBWYbwdd9-NqsSnueeveBK=_yh8vr=LKD+1djGyJg@mail.gmail.com обсуждение исходный текст |
| Ответ на | [GENERAL] hard parse? (Peter Koukoulis <pkoukoulis@gmail.com>) |
| Ответы |
Re: [GENERAL] hard parse?
|
| Список | pgsql-general |
HiI have a query where a filter would always be negative, how many steps, out these:
- parsing and syntax check
- semantic analysis
- transformation process (query rewrite based on system or user-defined rules)
- query optimization
- execution
would be performed or not? Also, where in the documentation can I found out which of the above phases would be performed?For example, for a query such as the following:select x,y from test1 where 1=0;
I'm inferring behavior here but...
All of them. You are still going to get a result set with zero records and the correct column structure. i.e., "Execution". None of the other stuff can be skipped in getting to engine to that point. With a "always false" predicate and that simple of a query structure most of the other stuff, including execution, is probably performed is seemingly zero time but it still has to work through that step of the process - if nothing else than to move through an if-branch to decide that nothing material needs to be done.
David J.
В списке pgsql-general по дате отправления: