On Thu, May 6, 2021 at 10:38 AM Semen Yefimenko <semen.yefime...@gmail.com> wrote:
> Hi there, > > I've recently been involved in migrating our old system to SQL Server and > then PostgreSQL. Everything has been working fine so far but now after > executing our tests on Postgres, we saw a very slow running query on a > large table in our database. > I have tried asking on other platforms but no one has been able to give me > a satisfying answer. > ... > > SELECT column1,..., column54 where ((entrytype = 4000 or entrytype = 4001 > or entrytype = 4002) and (archivestatus <= 1)) order by timestampcol desc; > > > I know several people have suggested using `IN` to replace the or statements, that would be my first go-to also. Another approach I have found helpful is to keep in mind whenever you have an `OR` in a where clause it can be replaced with a `UNION ALL`. Usually the `UNION ALL` is faster. I recommend avoiding `OR` in where clauses as much as possible. - Sometimes it can't be helped, especially if you need an exclusive or, but most of the time there is another way that is usually better. Another thought is "archivestatus" really a boolean or does it have multiple states? If it is actually a boolean, then can you change the column data type?
