Question

在此联接查询中，我将来自不同表格的两列相乘premium＆amp; points。我想要发生的是，如果premium表中没有列加入，则乘数将为1.

这是查询

 SELECT parent.*,(premiumtable.bid * pointstable.points) as total FROM strings parent
        LEFT JOIN premium premiumtable on parent.sid=premiumtable.sid AND premiumtable.paid='1'
        LEFT JOIN points pointstable on parent.sid=pointstable.`string-id`
        WHERE parent.category=:category AND (parent.submittype='0' OR parent.submittype='3') GROUP BY parent.id ORDER BY total LIMIT 5

因此，如果premiumtable上没有任何内容加入premiumtable.bid * pointstable.points而不是1 * pointstable.points，那么它就会premiumtable.bid。 total充当乘数，如果不存在，我希望pointstable.points等于{{1}}

Answer 1

使用case声明：

SELECT parent.*,
       case when premiumtable.bid is null
            then pointstable.points
            else premiumtable.bid * pointstable.points
       end as total 
FROM strings parent
LEFT JOIN premium premiumtable on parent.sid=premiumtable.sid AND premiumtable.paid='1'
LEFT JOIN points pointstable on parent.sid=pointstable.`string-id`
WHERE parent.category=:category
AND (parent.submittype='0' OR parent.submittype='3')
GROUP BY parent.id
ORDER BY total
LIMIT 5

Answer 2

尝试使用COALESCE：

SELECT   parent.*,
         (COALESCE(premiumtable.bid,1) * pointstable.points) as total 
FROM strings parent
LEFT JOIN premium premiumtable 
   on parent.sid=premiumtable.sid AND premiumtable.paid='1'
LEFT JOIN points pointstable 
   on parent.sid=pointstable.`string-id`
WHERE parent.category=:category 
AND (parent.submittype='0' OR parent.submittype='3') 
GROUP BY parent.id 
ORDER BY total LIMIT 5

乘以两列，不同的表......一列为空

2 个答案: