Why outer order by does not work correctly?

问题

I have a query like this:

SELECT @rank := @rank + 3 `rank`, id, subject, name
  FROM quran, (select @rank := -2) q
     WHERE MATCH (subject, name) AGAINST ('anything') and aye IN ("10")

UNION DISTINCT

SELECT @rank1 := @rank1 + 3 `rank`, id, subject, name
  FROM quran, (select @rank1 := -1) q 
     WHERE MATCH (subject, name) AGAINST ('anything')

UNION ALL

SELECT @rank2 := @rank2 + 3 `rank`, id, subject, byA
  FROM hadith, (select @rank2 := 0) q 
     WHERE MATCH (subject) AGAINST ('anything')

ORDER BY rank LIMIT 0, 11

Now I optimized my query and combined tow first SELECT clause to one, like this: (because they have the same table name)

(SELECT @rank1 := @rank1 + 2 `rank`, id, subject, name
  FROM quran, (select @rank1 := -1) q 
     WHERE MATCH (subject, name) AGAINST ('anything') 
       ORDER BY CASE WHEN aye IN ('10') 
          THEN 0
          ELSE 1
       END
)

UNION ALL

(SELECT @rank2 := @rank2 + 2 `rank`, id, subject, byA
  FROM hadith, (select @rank2 := 0) q 
     WHERE MATCH (subject) AGAINST ('anything')
)

ORDER BY rank LIMIT 0, 11

But I don't know why the sort of result is not identical with the first query. Why? And how can I fix it?

Edit: Here is some examples:

// quran                               // hadith
+----+---------+--------+                +----+---------+-------+
| id | subject |  name  |                | id | subject |  byA  |
+----+---------+--------+                +----+---------+-------+
| 1  | hello   | jack   |                | 1  | blue    | jack  |
| 2  | blue    | peter  |                | 2  | how     | hello |
| 3  | jack    | red    |                | 3  | jack    | blue  |
| 4  | back    | blue   |                +----+---------+-------+
| 10 | jack    | how    |
+----+---------+--------+

Now, I want this output: So first priority is that $number, and then subject column and then name column, Also the result is alternating for both tables.

$anything = 'jack', $number = 10
+----+---------+--------+
| id | subject |  name  |
+----+---------+--------+
| 10 | jack    | how    |
| 3  | jack    | blue   |
| 3  | jack    | red    |
| 1  | blue    | jack   |
| 1  | hello   | jack   |
+----+---------+--------+

回答1:

I'm not saying this is the best way to go about things, but it is the least modification to your existing attempts.

(
  SELECT IF(aye IN ("10"), 0, 1) AS sortGroup
     , IF(aye IN ("10"), @rank := @rank + 3, @rank1 := @rank1 + 3) AS `rank`
     , id, subject, name
  FROM quran
     , (select @rank := -2) AS rq, (select @rank1 := -1) AS r1q  
  WHERE MATCH (subject, name) AGAINST ('anything') 
)
UNION ALL
(
  SELECT 2 AS sortGroup
     , @rank2 := @rank2 + 2 `rank`
     , id, subject, byA
  FROM hadith
     , (select @rank2 := 0) AS q 
  WHERE MATCH (subject) AGAINST ('anything')
)
ORDER BY sortGroup, rank 
LIMIT 0, 11

Actually, I am not positive you can merge the first two unioned queries and get the same results. In the original query, with UNION DISTINCT and the separate computation of rank in the original, records that satisfy the aye IN ("10") criteria will probably often appear twice (but with different rank values).

来源：https://stackoverflow.com/questions/33174052/why-outer-order-by-does-not-work-correctly

标签

mysql

performance

sql-order-by

union-all