[英]SQL query to join 4 Tables and get sum of 2 columns from 2 different tables
[英]SQL get the sum of entries from join tables
我在mysql中越深入,我迷失的就越多,而现在我迷失了。 所以我有一些桌子:
主表
id|message|name
-----------------
1 |test |OP
2 |test2 |jim
3 |test3 |ted
表格1
id|likes
---------
2 | 1
3 | 0
表2
id|likes
---------
2 | 1
表3
id|likes
---------
1 | 1
2 | 1
3 | 0
我想要做的是获取一列中每个ID的likes
总数(其中一个等于1),这样我就可以计算一条消息的总数(带有其各自的ID)。
到目前为止,我已经成功地加入了我的表,所以最后我得到了一个likes
专栏:
SELECT id,Table1.likes,Table2.likes,Table3.likes
FROM MainTable
LEFT JOIN Table1.id ON MainTable.id = Table1.id LEFT JOIN Table2.id ON MainTable.id = Table2.id LEFT JOIN Table3.id ON MainTable.id = Table3.id
首先,有可能吗? 我知道我的代码不是很好,但至少是一个开始!
谢谢!
我猜您正在寻找其中之一...
SELECT
id
,SUM(Table1.likes)
,SUM(Table2.likes)
,SUM(Table3.likes)
FROM MainTable
LEFT JOIN Table1 ON MainTable.id = Table1.id
LEFT JOIN Table2 ON MainTable.id = Table2.id
LEFT JOIN Table3 ON MainTable.id = Table3.id
GROUP BY MainTable.id
SELECT
id
,SUM(Table1.likes)+SUM(Table2.likes)+SUM(Table3.likes)
FROM MainTable
LEFT JOIN Table1 ON MainTable.id = Table1.id
LEFT JOIN Table2 ON MainTable.id = Table2.id
LEFT JOIN Table3 ON MainTable.id = Table3.id
GROUP BY MainTable.id
这是查询,为MainTable中的每一行计算非零赞数:
SELECT
MainTable.id,
MainTable.name,
MainTable.message,
COUNT(Table1.likes) + COUNT(Table2.likes)
+ COUNT(Table3.likes) AS n_likes
FROM
MainTable
LEFT JOIN
Table1 ON MainTable.id = Table1.id
AND
Table1.likes=1
LEFT JOIN
Table2 ON MainTable.id = Table2.id
AND
Table2.likes=1
LEFT JOIN
Table3
ON
MainTable.id = Table3.id
AND
Table3.likes=1
GROUP BY
MainTable.id;
当心,您的SQL语法有错误:
LEFT JOIN Table1.id
联接时,必须写表名,不带列:
LEFT JOIN Table1
您可以使用UNION ALL来解决此问题。
请参阅以下测试。
CREATE TABLE `test`.`items` (
`id` INT NOT NULL ,
`message` VARCHAR(45) NULL ,
`name` VARCHAR(45) NULL ,
PRIMARY KEY (`id`) );
insert into items values
(1, "Message 1", "OP"),
(1, "Message 2", "jim"),
(1, "Message 3", "ted");
CREATE TABLE `test`.`table1` (
`id` INT NOT NULL ,
`likes` INT(10),
PRIMARY KEY (`id`) );
CREATE TABLE `test`.`table2` (
`id` INT NOT NULL ,
`likes` INT(10),
PRIMARY KEY (`id`) );
CREATE TABLE `test`.`table3` (
`id` INT NOT NULL ,
`likes` INT(10),
PRIMARY KEY (`id`) );
insert into table1 values
( 2, 1),
( 3, 0);
insert into table2 values
( 2, 1),
( 3, 0);
insert into table3 values
(1,1),
(2,1),
(3,0);
select source.id, sum(likes)
from (
select id, likes from table1 as t1
UNION ALL
select id, likes from table2 as t2
UNION ALL
select id, likes from table3 as t3
) as source group by id;
输出量
1, 1
2, 3
3, 0
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