Re: update from select

["Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com>]

Hello

you use corelated subquery and that is slow for thausands rows. Use
PostgreSQL's extension

UPDATE table1 SET column2 = t,colum2, ....
FROM table2 t
WHERE table1.column1 = t.column1 and t.column4 is not null and ...

http://www.postgresql.org/docs/8.2/interactive/sql-update.html

Regards
Pavel Stehule

> Hello
>
>
>
> I have a performance problem with an SQL statement.
>
> Is there a better way to do this update:
>
>
>
> UPDATE table1 SET column2 = temp_table.column2, column3 =
> temp_table.column3, column4 = CAST(temp_table.column4 AS date) FROM
>
> (
>
>  SELECT DISTINCT
>
>  table2.column1,
>
>  table2.column2,
>
>  table2.column3,
>
>  table2.column4
>
>  FROM table2 WHERE column4 IS NOT NULL AND column4 <> '' AND
> (length(column4) = 10 OR length(column4) = 23)
>
> ) AS temp_table
>
> WHERE table1.column1 = temp_table.column1;
>
>
>
> The select by it's own takes around 1 second. The Update is around 120'000
> rows. I got an index on column1. The whole query needs around 16 minutes.
>
> The same procedure on MSSQL needs around 30 seconds. I hope to get it too in
> Postgres…
>
>
>
> Please help me.
>
>
>
> Regards
>
>
>
> Reto
>
>