Question

I have a column with a string in it, and due to a bug some of the string values are wrong. So I want to fix the strings by taking the original string and concatenating information from a select to it. Ideally it would be something like:

UPDATE table as t
SET t.string = SELECT CONCAT(t.string, 
                             (SELECT fix FROM othertable where id=t.id )
                            );

But of course, I can’t do that using concat.
I have to say I’ve not got very far with any other method.
Anyone have an ideas?

Answer 1

If the subquery is guaranteed to return just one value, you could simply drop the SELECT keyword before CONCAT:

UPDATE table as t
SET t.string = CONCAT(t.string, 
                      (SELECT fix FROM othertable where id=t.id)
                     );

If the subquery may return more than one value, a quick fix could be to apply GROUP_CONCAT like this:

UPDATE table as t
SET t.string = CONCAT(t.string, 
                      (SELECT GROUP_CONCAT(fix) FROM othertable where id=t.id)
                     );