Question

2Been花了几个小时在这上面，它对我来说没问题。我究竟做错了什么。我的数据库看起来像这样。

id, type_name
1, 1
2, 3
3, 1
4, 1
5, 2
6, 3

我的查询看起来像这样。

SELECT
DISTINCT(p.`id`) as id,
count (p1.type_name) as L1,
count (p2.type_name) as L2,
count (p3.type_name) as L3
FROM
proxylist AS p

LEFT JOIN (SELECT `id`,`type_name`, count(`type_name`) as L1
WHERE `type_name` = 1) as p1 
ON p1.`id` = p.`id`

LEFT JOIN (SELECT `id`,`type_name`, count(`type_name`) as L1
WHERE `type_name` = 3) as p2 
ON p2.`id` = p.`id`

LEFT JOIN (SELECT `id`,`type_name`, count(`type_name`) as L1
WHERE `type_name` = 3) as p3 
ON p3.`id` = p.`id`

GROUP BY p.`id`

我收到错误＆＃34; [Err] 1064 - 您的SQL语法出错了;检查与您的MySQL服务器版本对应的手册，以获得正确的语法，以便在＆＃39; count（type_name）附近使用为L1 WHERE type_name = 1）为p1 在第1页。id = p。id＆＃34;

Answer 1

我认为你只想要条件聚合：

SELECT p.id,
       SUM(p.type_name = 1) as L1,
       SUM(p.type_name = 2) as L2,
       SUM(p.type_name = 3) as L3
FROM proxylist p
GROUP BY p.id;

我相当确定您的查询会针对三个计算值返回1或0。以上是对你可能要做的事情的合理猜测。

MySql子选择尝试获取列值的计数

1 个答案: