MySQL update with correlated query on the same table

husakg :

The problem can be simplified as follows:

Original state:

id   type   val
---------------
1    1      300
2    1      200
3    1      100
4    2      10
5    2      20
6    2      30

Desired state - for a range of ids (here 3 to 4), update val so that it's equal to the maximum val for the given type:

id   type   val
---------------
1    1      300
2    1      200
3    1      300  <--
4    2      30   <--
5    2      20
6    2      30

So only rows 3 and 4 were updated, maximum val for type 1 is 300, for type 2 it's 30.

I thought it's an easy update, but I can't get it to work.

Here's the table definition and data:

create table test (id integer primary key, type integer, val integer);
insert into test (id, type, val) values (1, 1, 300);
insert into test (id, type, val) values (2, 1, 200);
insert into test (id, type, val) values (3, 1, 100);
insert into test (id, type, val) values (4, 2, 10);
insert into test (id, type, val) values (5, 2, 20);
insert into test (id, type, val) values (6, 2, 30);

And here's what I thought would work:

update test t1 set t1.val=(
  select max(t2.val) from (
    select * from test where type=t1.type
  ) t2
) where id>=3 and id<5;

However MySQL gives the error:

Unknown column 't1.type' in 'where clause'

I've found some answers to similar problems suggesting rewriting the update so that it uses JOIN, but I'm not sure how to do that - my attempt resulted in an error message about a nonexisting table. Please tell me what I'm missing.

tcadidot0 :

Try this query:

UPDATE test t1 INNER JOIN
(SELECT TYPE,MAX(val) mval FROM test GROUP BY TYPE) t2
ON t1.type=t2.type
SET t1.val=t2.mval
WHERE t1.id BETWEEN 3 AND 4;

Fiddle here : https://www.db-fiddle.com/f/7Sn9aDBPze7pVvHNHFzQ1u/2