Question

我需要生成如下所述的表格。我有这些样品，但它不起作用。任何请帮助。

SELECT id, room, bed, 
bed -(SELECT count(bed) FROM tb_student WHERE room_id = id) as FREE
FROM tb_rooms

tb_rooms
+----+-------+-----+
| ID | ROOM  | BED |
+----+-------+-----+
|  1 | A111  |  4  |
|  2 | A112  |  2  |
|  3 | A113  |  2  |
|  4 | A114  |  2  |
+----+-------+-----+

tb_student
+----+---------+----------+
| ID | STUD_ID  | ROOM_ID |
+----+---------+----------+
|  1 |    211   |  3      |
|  2 |    212   |  1      |
|  3 |    213   |  1      |
|  4 |    214   |  2      |
+----+----------+---------+

I need something like this...
+----+-------+------+-----+
| ID | ROOM  | BED  |FREE |
+----+-------+------+-----+
|  1 | A111  |  4   | 2   |
|  2 | A112  |  2   | 1   |
|  3 | A113  |  2   | 1   |
|  4 | A114  |  2   | 2   |
+----+-------+------+-----+

Answer 1

试试这个

 SELECT id as id, room as room, bed as bed, 
 bed -( SELECT count(Room_ID) FROM tb_student where room_id = soh.id) as FREE
 FROM tb_rooms soh

祝你好运

Answer 2

你好john你的查询权限只创建你的表的别名看到你的问题：

    SELECT id as id, room as room, bed as bed, 
bed -( SELECT count(*) FROM tb_student where room_id = tr.id) as FREE
FROM tb_rooms tr

Answer 3

你可以试试这个：

SELECT
  r.ID, 
  r.ROOM, 
  r.BED,
  r.BED - COUNT(DISTINCT s.ID) AS FREE
FROM tb_rooms AS r
  LEFT JOIN tb_student AS s ON r.ID = s.ROOM_ID
GROUP BY r.ID, r.ROOM, r.BED

这是SQLFIDDLE。

SQL查询COUNT SELECT

3 个答案: