java - MySQL这样的两个表，如何让b表的某一个字段的数量作为a表的一条记录的一个值，写道这里不会了？

Question

让B表中bd_id 跟A表id一样的做一个总数作为A标的bd_xl_zs(标的线路总数) ，我写的查询语句如下

SELECT
    bd_name,
    bd_bz,
    (
        SELECT
            COUNT(bd_id)
        FROM
            bhwl_zbgl_bd_child
        WHERE
            `status` = 0
        AND bd_id =***这里不知道怎么写***
    ) AS bd_xl_zs
FROM
    bhwl_zbgl_bd
WHERE
    `status` = 0

Answer 1

SELECT a.bd_name, a.bd_bz, count(b.bd_id)
FROM xxx a, xxx b
WHERE a.id = b.bd_id and a.status = 0
GROUP BY b.bd_id

Answer 2

select a.,b. from a inner join ( select bd_id,count(bd_id)
from b where status = 0 group by bd_id) b on a.id = b.bd_id

Answer 3

Group by bd_id