Loop to run multiple updates from different tables in postgres

Question

I am running Postgres 9.1 and have a master table (returns.msf_mse) with 30 empty columns and 30 additional temporary tables (temp23_01 - temp23_30). I want to populate each of the empty columns in the master table with the data from a particular column from each temporary table. The relevant column in each temporary table is always cumret_past.

I have tried to create a stored procedure/function to achieve this and have been getting nowhere. I have also tried to loop over the update statement but can not get it to work. My base query is:

update returns.msf_mse as a
set cumret_past_23_01 = b.cumret_past  
from temp23_01 as b
where a.date = b.date
and a.permno = b.permno;

I simply want to run this statement 30 times, incrementing cumret_past_23_i and temp23_i each time.

Answer 1

You could use a DO statement (pg 9.0+) with EXECUTE to loop through all tables:

DO
$$
BEGIN

FOR i IN 1..30 LOOP
    EXECUTE '
    UPDATE returns.msf_mse a
    SET    cumret_past_23_' || to_char(i, 'FM00') || ' = b.cumret_past  
    FROM   temp23_' || to_char(i, 'FM00') || ' b
    WHERE  a.date = b.date
    AND    a.permno = b.permno';
END LOOP;

END
$$

Pay attention to the leading space when formatting the number with to_char(). I use the FM modifier to get rid of it.

Aside: I wouldn't use date as column name, it easily conflicts with the base type or the function of the same name.