Mysql - UPDATE表SET列= SELECT COUNT（*）FROM（SELECT * FROM table2 WHERE table2.id = table.id））不可能

Question

I have two tables with a lot of rows and I need to maintain "index" informations for each row in the first (table_1). So I wrote a query to not use directly COUNT() [wich is slow, slow, slow]. So I try :

UPDATE table_1 SET table_1.column_3 = (  
    SELECT COUNT(*) FROM (
        SELECT DISTINCT column_5 FROM table_2 WHERE table_2.id_t1 = table_1.id LIMIT 300
    ) t
)

But MySQL answering me that table_1.id is unknow in where clause (#1054)

Did you know how to passs table_1.id in the where clause ? Or other way to get my goal ?

Thank you for helping me !

Answer 1

the problem is because table_1 is too far from inner query, use:

UPDATE table_1 SET table_1.column_3 = 
(SELECT count(DISTINCT column_5) FROM table_2 WHERE table_2.id_t1 = table_1.id);

as I see you're using LIMIT, not really sure that you need it, anyway you can emulate it:

IF(count(distinct column_5)>300, 300, count(distinct column_5))