Question

我有这样的查询

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

现在我只想在联合之前的第一个查询上使用order by

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

但不起作用

我也用过

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

但是它也按顺序包含第二个查询，并且它也改变了位置，我不希望仅在第一个查询上对第二个查询进行排序。

Answer 1

您不能订购UNION的“零件”；即使您尝试通过子查询强制使用它，MySQL也会忽略它。但是，您可以创建一个额外的订购字段。这是此方法的通用模板：

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

不，您不需要subquery：

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

相反，我会像使用单个SELECT语句那样重写：

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

您需要编写一个子查询，并在第一个查询和第二个查询上标记seqnum，然后在order by和seqnum上使用多个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

在mysql中对联合的一个查询进行排序

4 个答案: