带有union join或left join的SQL语句

Question

database table

我有这个SQL问题来查找2表

之间禁用人员的总数

条件是我只想让ID出现在收件人表中

left join graph

我只想获得与a_children链接在一起的左侧数据的总数

Answer 1

http://sqlfiddle.com/#!9/2ca178/1

SELECT COUNT(*)
FROM recipient r
LEFT JOIN a_children c
ON r.hp_id = c.hp_id
   AND c.health='OKU'
WHERE r.disability = 'YES'