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
结果
+------+--------------+--------+
| name | PriceTotal | id_cat |
+------+--------------+--------+
| Cat1 | 1031.40 | 1 |
| Cat2 | 200.88 | 2 |
| Cat4 | 46.44 | 4 |
| Cat5 | 223.76 | 5 |
+------+--------------+--------+
问题是我有 4 个以上的类别,我尝试了不同的连接,但它们不会显示 PriceTotal 为空值的类别 1-7。
我真的不知道该怎么做
+------+--------------+--------+
| 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 |
+------+--------------+--------+
最佳答案
左连接的 2 个选项:
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
或:
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
关于mysql - 在 join | 中显示空值销售值(value) - 类别,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45693841/