Mysql 在联接|销售价值-类别中显示空值
结果Mysql 在联接|销售价值-类别中显示空值,mysql,sql,Mysql,Sql,结果 SELECT cat_tbl.id_cat, cat_tbl.name, Sum(expences.price) AS PriceTotal FROM cat_tbl JOIN expences ON cat_tbl.id_kat= expences.category GROUP BY cat_tbl.id_cat, cat_tbl.name 问题是,我有4个以上的类别,我尝试了不同的联接,但它们不会显示类别1-7以及PriceTotal的
SELECT
cat_tbl.id_cat,
cat_tbl.name,
Sum(expences.price) AS PriceTotal
FROM cat_tbl
JOIN expences ON cat_tbl.id_kat= expences.category
GROUP BY
cat_tbl.id_cat,
cat_tbl.name
问题是,我有4个以上的类别,我尝试了不同的联接,但它们不会显示类别1-7以及PriceTotal的空值
我真的不知道怎样才能做到这一点
+------+--------------+--------+
| name | PriceTotal | id_cat |
+------+--------------+--------+
| Cat1 | 1031.40 | 1 |
| Cat2 | 200.88 | 2 |
| Cat4 | 46.44 | 4 |
| Cat5 | 223.76 | 5 |
+------+--------------+--------+
2个左连接选项:
+------+--------------+--------+
| name | PriceTotal | id_cat |
+------+--------------+--------+
| Cat1 | 1031.40 | 1 |
| Cat2 | 200.88 | 2 |
| Cat3 | 0 | 3 |
| Cat4 | 46.44 | 4 |
| Cat5 | 223.76 | 5 |
| Cat6 | 0 | 6 |
| Cat7 | 0 | 7 |
+------+--------------+--------+
或:
选择ct.id\u cat、ct.name、Sum(不含价格)作为PriceTotal
来自cat_tbl ct
连接ct上的费用ex.id\u cat=ex.category
左连接费用ex2开启(ct.id\U cat=ex2.category和ex.category
使用左连接
而不是简单的连接
。我知道,我也尝试过,但结果没有改变。你确实需要使用外部连接
,这不是信仰或其他问题。之后,您需要修复其他阻止您看到正确结果的错误。下面是一个例子,展示了简化的案例。下一次,请看:@草莓可以,但我认为它是非常通用的。第一个案例不应该是类似于SUM(COALESCE(expenses.price,0))
?可爱的第二个答案;)@johnHC如果我想介绍WHERE语句,它必须在两个地方都出现吗?比如在哪里约会Between@KavvsonEmpcraft这取决于日期适用于哪个表。如果两者都适用,则将其添加到两者。否则,如果是Cat,则添加到整个查询的末尾,如果是Exp,则添加到子查询中。好的,谢谢,它将应用到expense请添加一些上下文,说明为什么您的代码应该解决此问题。
SELECT
cat_tbl.id_cat,
cat_tbl.name,
Sum(expences.price) AS PriceTotal
FROM cat_tbl
LEFT JOIN expences
ON cat_tbl.id_kat= expences.category
GROUP BY
cat_tbl.id_cat,
cat_tbl.name
select cat.id_cat, cat.name,
coalesce(exp.tot, 0) as PriceTotal
from cat_tbl cat
left join
(
select x.category, sum(x.price) as tot
from expences x
group by x.category
) exp
on cat.id_cat = exp.category
SELECT ct.id_cat, ct.name, Sum(ex.price) AS PriceTotal
FROM cat_tbl ct
JOIN expences ex ON ct.id_cat= ex.category
LEFT JOIN expences ex2 ON (ct.id_cat = ex2.category AND ex.category < ex2.category)
.....
WHERE ex2.category IS NULL