交替选择行从另一个表

Question

有序域给出一个* students_exam_rooms *表：

+------------+---------+---------+ 
| student_id | room_id | seat_no | 
+------------+---------+---------+ 
|   1 |  30 | 1001 | 
|   2 |  30 | 1002 | 
|   3 |  31 | 2001 | 
|   4 |  32 | 2002 | 
|   5 |  33 | 3001 | 
|   6 |  33 | 3002 | 
|   7 |  34 | 4001 | 
|   8 |  34 | 4002 | 
+------------+---------+---------+ 

而* students_tbl *：

+------------+-------------+------+ 
| student_id | studen_name | year | 
+------------+-------------+------+ 
|   1 | Eric  | 1 | 
|   2 | Mustafa  | 1 | 
|   3 | Michael  | 2 | 
|   4 | Andy  | 2 | 
|   5 | Rafael  | 3 | 
|   6 | Mark  | 3 | 
|   7 | Jack  | 4 | 
|   8 | peter  | 4 | 
+------------+-------------+------+ 

如何从* students_exam_rooms选​​择*由* students_tbl排序.year *但是一个接一个是这样的：

+--------------+------+ 
| student_name | year | 
+--------------+------+ 
| Eric   | 1 | 
| Michael  | 2 | 
| Rafael  | 3 | 
| Jack   | 4 | 
| Mustafa  | 1 | 
| Andy   | 2 | 
| Mark   | 3 | 
| Peter  | 4 | 
+--------------+------+ 

Answer 1

请尝试以下任意一项：

SELECT a.studen_name, a.year 
FROM students_tbl a 
     INNER JOIN students_exam_rooms b 
      ON a.student_id = b.student_id 
ORDER BY REVERSE(b.seat_no), 
      a.year 

• SQLFiddle Demo

使用Modulo

SELECT a.studen_name, a.year 
FROM students_tbl a 
     INNER JOIN students_exam_rooms b 
      ON a.student_id = b.student_id 
ORDER BY CASE WHEN MOD(b.seat_no, 2) <> 0 THEN 0 ELSE 1 END, 
      a.year 

• SQLFiddle Demo

Answer 2

我假设你はnt按照年份和年份的“发生次数”排序，例如所有年份中首次出现的所有年份，按年份排序，然后所有年份中的所有次数也按年份排序，依此类推。这将是仿效其他RDBMS”分析/窗口化功能的完美案例：

select * 
from (
    select 
     s.studen_name, 
     s.year, 
     ser.*, 
     (
      select 1 + count(*) 
      from students_tbl s2 
      where s.year = s2.year 
       and s.student_id > s2.student_id 
     ) rank 
    from students_tbl s 
     JOIN students_exam_rooms ser 
      ON s.student_id = ser.student_id 
) i_dont_really_want_to_name_this 
order by rank, year 

这对JW的小提琴轻微扭捏版本：http://www.sqlfiddle.com/#!2/27c91/1

Emulating Analytic (AKA Ranking) Functions with MySQL是一个很好的文章，让更多的背景和说明。

Answer 3

在我看来，你试图按座位排序，然后按年排序。看看你的students_exam_rooms表格，它看起来像是从一个简单的座位号开始的，并且以前为year * 1000。所以，如果我们忽略的一年，它看起来像这样：

> select * from fixed_students_exam_rooms; 
+------------+---------+---------+ 
| student_id | room_id | seat_no | 
+------------+---------+---------+ 
|   1 |  30 |  1 | 
|   2 |  30 |  2 | 
|   3 |  31 |  1 | 
|   4 |  32 |  2 | 
|   5 |  33 |  1 | 
|   6 |  33 |  2 | 
|   7 |  34 |  1 | 
|   8 |  34 |  2 | 
+------------+---------+---------+ 

如果你有是表，查询很简单：

select 
    student_name, year 

from 
    modified_student_exame_rooms 
    left join students_tbl using (student_id) 

order by 
    seat_no, year 
; 

使用表，你现在有它，它只是稍微复杂一些，假设“核心座位号”不excede 999

select 
    student_name, year 

from 
    modified_student_exame_rooms 
    left join students_tbl using (student_id) 

order by 
    convert(substr(seat_no, 2), unsigned), 
    year 
;