[postgis-users] Setting multiple columns in one UPDATE request

Marco Boeringa marco at boeringa.demon.nl
Sun Sep 27 00:28:34 PDT 2020

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 

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?


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