在mysql中对联合的一个查询进行排序

Question

I have a query like this

SELECT t.id,t.name,t.count 
FROM Teacher 
UNION 
SELECT '','',(SELECT count(*) FROM student)

Now I want to use order by only on the first query before union like this

SELECT t.id,t.name,t.count 
FROM Teacher 
ORDER BY t.name ASC
UNION 
SELECT '','', (SELECT count(*) FROM student)

but it does not work

I have also used

SELECT *
FROM (SELECT t.id,t.name,t.count FROM Teacher) as teacher 
UNION 
SELECT '','',(SELECT count(*) FROM student) 
ORDER BY name ASC

but it includes the second query also in the order by and it changes its position also and I don't want order by on the second query only on the first.

Answer 1

You cannot order "parts" of a UNION; even if you try to force it with subqueries, MySQL will just disregard it. You can create an extra ordering field though. here is a generic template for this method:

SELECT u.A, u.B, u.C
FROM
(
   SELECT 0 as seq, A, B, C
   FROM table1
   UNION 
   SELECT 1 AS seq, A, B, C
   FROM table2
) AS u
ORDER BY u.seq

Answer 2

No, you can't you need subquery :

SELECT *
FROM (SELECT id, name, count 
      FROM Teacher 
      UNION 
      SELECT '', '', (SELECT count(*) FROM student)
     ) t
ORDER BY name;

Instead, i would rewrite as with single SELECT statement :

SELECT *
FROM (SELECT id, name, count 
      FROM Teacher 
      UNION 
      SELECT '', '', count(*) 
      FROM student
     ) t
ORDER BY name;

Answer 3

尝试使用（），它将使您仅在第一次查询时就订购

(SELECT t.id,t.name,t.count FROM Teacher ORDER BY t.name ASC) UNION (SELECT '','', (SELECT count(*) FROM student)) 

Answer 4

You need write a subquery and make seqnum mark first query and second query then use multiple order by on seqnum and name

SELECT t.*
FROM (
        SELECT 1 seqnum,t.id,t.name,t.count 
        FROM Teacher 
        UNION 
        SELECT 2,'','', (SELECT count(*) FROM student)
     ) t
ORDER BY t.seqnum,t.name