mysql根据一个表更新另外一个表

-- 语法：update table_1 t1,table_2 t2 set t1.column = t2.column where t1.id = t2.pid;

UPDATE house_test.shareInfo AS t1,
(
    SELECT
        u.*,
        g.city_code 
    FROM
        `api`.`user` AS u
        LEFT JOIN `api`.`group` AS g ON g.group_id = u.group_id 
    ) AS t2 
    SET t1.cityCode = t2.city_code 
WHERE
    t1.userId = t2.user_id 
    AND (
        t1.cityCode IS NULL 
    OR t1.cityCode = '')