Question

I have 2 tables: legend and temp. temp has an ID and account ID, legend has advent_id, account_id and other columns. ID in temp and advent_id in legend are similar. account_id column is empty and I want to import the relevant account_id from temp to legend. I am using PostgreSQL.

I am trying the following query, but it is not working as I am expecting. New rows are getting created and the account_id’s are getting added in the new rows, not to the corresponding advent_id.

insert into legend(account_id)
select temp.account_id
from legend, temp
where legend.advent_id=temp.id;

It is inserting the account_id in the wrong place, not to the corresponding advent_id.

I am using the following query to check:

select advent_id, account_id from legend where account_id is not null;

What exactly is the problem in my insert query?

Answer 1

If you are trying to modify existing rows, rather than add rows, then you need an UPDATE query, not an INSERT query.

It’s possible to use joined tables as the target of an UPDATE; in your example:

UPDATE legend
JOIN temp
SET legend.account_id = temp.account_id
WHERE(temp.id = legend.advent_id);