MySQL SELECT到VIEW返回不同的结果

Question

I have put together a small sql query which brings data from one table and sorts it under new column names. The sql looks like this:

SELECT course_id AS course, NOW() as datum,
(SELECT COUNT(*) FROM users_courses WHERE course_id = course) AS antal_registrerade,
(SELECT COUNT(*) FROM users_courses WHERE status = 1 AND course_id = course) AS antal_aktiva,
(SELECT COUNT(*) FROM users_courses WHERE status = 3 AND course_id = course) AS antal_avklarade
FROM users_courses GROUP BY course_id

The above query returns the following:

| course | datum               | antal_registrerade | antal_aktiva  | antal_avklarade   |
-----------------------------------------------------------------------------------------
| 31     | 2016-01-12 16:24:58 | 142                | 19            | 83                |
| 38     | 2016-01-12 16:24:58 | 826                | 45            | 49                |
| 39     | 2016-01-12 16:24:58 | 2                  | 2             | NULL              |
| 43     | 2016-01-12 16:24:58 | 169                | 29            | 32                |
| 44     | 2016-01-12 16:24:58 | 11                 | 4             | 2                 |
| 45     | 2016-01-12 16:24:58 | 67                 | 8             | 7                 |
| 46     | 2016-01-12 16:24:58 | 2                  | 1             | 1                 |   

All good right? Just like I wanted it. BUT when I save this query as a view and run that the result is different. I get the same data for every row, except for the course and datum columns.

| course | datum               | antal_registrerade | antal_aktiva  | antal_avklarade   |
-----------------------------------------------------------------------------------------
| 31     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |
| 38     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |
| 39     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |
| 43     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |
| 44     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |
| 45     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |
| 46     | 2016-01-12 16:24:58 | 1219               | 108           | 174               |   

Anyone have any idea why this is? The sql found in the saved view looks like this:

SELECT `database`.`users_courses`.`course_id` AS `course`,now() AS `datum`,
(SELECT COUNT(0) from `database`.`users_courses` where (`database`.`users_courses`.`course_id` = `database`.`users_courses`.`course_id`)) AS `antal_registrerade`,
(SELECT COUNT(0) from `database`.`users_courses` where ((`database`.`users_courses`.`status` = 1) and (`database`.`users_courses`.`course_id` = `database`.`users_courses`.`course_id`))) AS `antal_aktiva`,
(SELECT COUNT(0) from `database`.`users_courses` where ((`database`.`users_courses`.`status` = 3) and (`database`.`users_courses`.`course_id` = `database`.`users_courses`.`course_id`))) AS `antal_avklarade`
FROM `database`.`users_courses`
GROUP BY `database`.`users_courses`.`course_id`

Answer 1

This is much simpler to express using conditional aggregation:

SELECT course_id AS course, NOW() as datum,
       COUNT(*) as antal_registrerade,
       SUM(status = 1) as antal_aktiva,
       SUM(status = 3) AS antal_avklarade
FROM users_courses
GROUP BY course_id;

This should fix the problem with your results.

For some reason, the saved code for the view has the correlation clause incorrect. My guess is that you don't have two columns in the table for course and course_id , so your first query isn't exactly what is going into the view. In any case, fix this using a simpler query.