You have the correct link. Here's an example. https://stackoverflow.com/questions/36908495/update-with-result-from-cte-postgresql
Get BlueMail for Android On Sep 27, 2020, 7:47 AM, at 7:47 AM, Marco Boeringa <ma...@boeringa.demon.nl> wrote: >Hi Alexander, > >I guess I could use the optional WITH clause that is part of UPDATE in >PostgreSQL?: > >https://www.postgresql.org/docs/12/sql-update.html > >It would have been nice to see an example of such usage in the >PostgreSQL help, but I'll figure it out. > >Marco > >Op 27-9-2020 om 13:59 schreef Alexander Gataric: >> Rewrite to have a CTE with the area calculations and join to the >table. >> >> Get BlueMail for Android <http://www.bluemail.me/r?b=16117> >> On Sep 27, 2020, at 2:29 AM, Marco Boeringa <ma...@boeringa.demon.nl >> <mailto:ma...@boeringa.demon.nl>> wrote: >> >> Hi all, >> >> This may be an irrelevant basic question, but I just cannot find >a clear >> answer to this, there is no documentation in the PostgreSQL docs >for >> UPDATE about this: >> >> In case I set multiple columns using some PostGIS function that >clearly >> has a (considerable) cost associated with it, and the value of >the first >> column being set is also needed to set the second column, does >> PostgreSQL automatically optimize this and re-use the value >already >> calculated for column 1 to set column 2's value, or is each >column's SET >> statement treated as independent entity? >> >> E.g. let's say I want to calculate both area, and the division of >area >> and perimeter, like: >> >> UPDATE <MY_TABLE> SET area = ST_Area(<GEOMETRY_COLUMN>), >area_perimeter >> = ST_Area(<GEOMETRY_COLUMN>) / ST_Perimeter(<GEOMETRY_COLUMN>) >> >> Will PostgreSQL only process 'ST_Area(<GEOMETRY_COLUMN>)' once in >this >> case, thus saving CPU load, or do I need to rewrite the SQL >statement >> somehow to achieve that? >> >> Marco >> >> >------------------------------------------------------------------------ >> >> postgis-users mailing list >> postgis-users@lists.osgeo.org >> https://lists.osgeo.org/mailman/listinfo/postgis-users >> >> >> _______________________________________________ >> postgis-users mailing list >> postgis-users@lists.osgeo.org >> https://lists.osgeo.org/mailman/listinfo/postgis-users > > >------------------------------------------------------------------------ > >_______________________________________________ >postgis-users mailing list >postgis-users@lists.osgeo.org >https://lists.osgeo.org/mailman/listinfo/postgis-users
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