获取其余行

Question

请参阅下面的SQL查询，它计算与numbers和business表匹配的总记录数。

SELECT N.mobile, B.name, count(*) as Total FROM records as R 
LEFT JOIN business as B ON B.id = R.business_id 
LEFT JOIN numbers as N ON N.id = R.numbers_id 
group by N.mobile, B.name 

未包括在结果中。然而，也有剩余的行（N.mobile, B.name），如何将它们与Total会是0？

Answer 1

你是说有没有在​​records入口business和numbers行，但要包括他们在伯爵？由于MySQL不支持FULL OUTER JOIN使用UNION得到你想要的结果：

SELECT N.mobile, B.name, count(*) as Total FROM records as R 
LEFT JOIN business as B ON B.id = R.business_id 
LEFT JOIN numbers as N ON N.id = R.numbers_id 
GROUP BY N.mobile, B.name 

UNION 

SELECT N.mobile, NULL, 0 
FROM numbers AS N 
LEFT JOIN records as R ON N.id = R.numbers_id 
WHERE r.numbers_id IS NULL 

UNION 

SELECT NULL, B.Name, 0 
FROM business AS B 
LEFT JOIN records as R ON B.id = R.business_id 
WHERE r.business_id IS NULL 

Answer 2

用户OUTER JOIN而不是INNER JOIN包括这些丢失的记录：

SELECT N.mobile, B.name, count(*) as Total 
FROM records as R 
OUTER JOIN business as B ON B.id = R.business_id 
OUTER JOIN numbers as N ON N.id = R.numbers_id 
group by N.mobile, B.name