用另一个表数据更新字段

多个列

UPDATE a,
 b
SET a.title = b.title,
 a. category= b.category
WHERE
    a.id = b.id

子查询

UPDATE shop  s
SET city_name = (
    SELECT
        name
    FROM
        city
    WHERE
        id = s.city_id
);

一个表的cout更新另一个表的字段

UPDATE shop a
SET a.goods_count = (
    SELECT
        b.counts
    FROM
        (
            SELECT
                mid,
                count(*) counts
            FROM
                goods
            WHERE
                is_delete = 0
            AND STATUS = 1
            GROUP BY
                mid
        ) b
    WHERE
        a.mid = b.mid
)