SQL查询内部联接的值为0 [英] SQL query inner join with 0 values

问题描述

我有这张桌子:

idSection   | idQuestion    | title     | enunciation | idScale
1           | 1             | title 1   | question 1  |    3      
1           | 1             | title 1   | question 1  |    3      
1           | 1             | title 1   | question 1  |    3      
1           | 1             | title 1   | question 1  |    2
1           | 1             | title 1   | question 1  |    5
1           | 2             | title 2   | question 2  |    1      
1           | 2             | title 2   | question 2  |    3      
1           | 3             | title 3   | question 3  |    1      

并有此表:

idScale   |       name 
   1      |      Very Bad
   2      |         Bad
   3      |         Good
   4      |      Very Good
   5      |      Excellent

我想要一张这样的桌子:

I wanted a table like this:

idSection   | idQuestion    | title     | enunciation | Total  | Name
1           | 1             | title 1   | question 1  |    0   |  Very Bad
1           | 1             | title 1   | question 1  |    0   |  Bad
1           | 1             | title 1   | question 1  |    3   |  Good
1           | 1             | title 1   | question 1  |    0   |  Very Good
1           | 1             | title 1   | question 1  |    1   |  Excellent
1           | 2             | title 2   | question 2  |    0   |  Very Bad
1           | 2             | title 2   | question 2  |    1   |   Bad
1           | 2             | title 2   | question 2  |    3   |  Good 
1           | 2             | title 2   | question 2  |    0   |  Very Good
1           | 2             | title 2   | question 2  |    0   |  Excellent

查询:

SELECT 
    t1.idSection, t1.idQuestion, t1.title, t1.enunciation, 
    COUNT(t1.idScale) as Total, t2.name 
FROM 
    table1 AS t1
INNER JOIN 
    table2 as t2 ON t2.idScale = t1.idScale
GROUP BY 
    t1.idSection, t1.idQuestion, t1.title, t1.enunciation, t2.name

其结果是查询:

idSection   | idQuestion    | title     | enunciation | Total  | Name
1           | 1             | title 1   | question 1  |    3   |  Good
1           | 1             | title 1   | question 1  |    1   |  Excellent
1           | 2             | title 2   | question 2  |    1   |   Bad
1           | 2             | title 2   | question 2  |    3   |  Good 

此问题是不会出现查询值为0的情况.

The problem with this is that query values ​​that are 0 don't appear.

推荐答案

我认为您正在寻找:

SELECT
  t1.idSection,
  t1.idQuestion,
  t1.title,
  t1.enunciation, 
  SUM(case when t1.idScale=t2.idScale then 1 else 0 end) as Total,
  t2.name
FROM
  table1 AS t1, table2 as t2
GROUP BY t1.idSection, t1.idQuestion, t1.title, t1.enunciation, t2.name, t2.idScale
ORDER BY t1.idSection, t1.idQuestion, t2.idScale

这不是INNER JOIN，而是笛卡尔式联接(table1的每一行都与table2的每一行相乘).我正在使用SUM来计算INNER JOIN成功的行数.

this is not an INNER JOIN, but it's a cartesian join instead (every row of table1 is multiplied for every row of table2). I'm using SUM to count the rows where the INNER JOIN would have succeeded.

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