如何从一个表中选择最后一行，然后更新另一个表的最后一行？

Question

I'm doing this

    UPDATE table1
    SET table1.col1 = table2.col2
    FROM table2 WHERE table1.id = (SELECT MAX(id) FROM table1) AND table2.ID = (SELECT MAX(ID) FROM table2);

I have a syntax error, but I don't know how to do it.

Answer 1

Assuming that id is unique in table1:

UPDATE table1 t1
    SET t1.col1 = (select t2.col2 from table2 t2 order by id desc limit 1) 
    ORDER BY t1.id DESC
    LIMIT 1;

This updates the "last" row in table1 (by id ) with the "last" row in table2 (by id ).

Your syntax doesn't work in multiple ways:

• MySQL does not support the FROM clause in UPDATE .
• MySQL does not allow you to reference the table being updated in a subquery.

Answer 2

MySQL

   update table1
    cross join (
        select col2
        from table2
        order by id desc
        limit 1) as A
    inner join (
        select id
        from table1
        order by id desc
        limit 1) as B on (B.id = table1.id)
    set table1.col1 = A.col2