问题
Is there a way in SQL (MySQL) to do a "round robin" ORDER BY on a particular field?
As an example, I would like to take a table such as this one:
+-------+------+
| group | name |
+-------+------+
| 1 | A |
| 1 | B |
| 1 | C |
| 2 | D |
| 2 | E |
| 2 | F |
| 3 | G |
| 3 | H |
| 3 | I |
+-------+------+
And run a query that produces results in this order:
+-------+------+
| group | name |
+-------+------+
| 1 | A |
| 2 | D |
| 3 | G |
| 1 | B |
| 2 | E |
| 3 | H |
| 1 | C |
| 2 | F |
| 3 | I |
+-------+------+
Note that the table may have many rows, so I can't do the ordering in the application. (I'd obviously have a LIMIT clause as well in the query).
回答1:
What you can do is create a temporary column in which you create sets to give you something like this:
+-------+------+-----+
| group | name | tmp |
+-------+------+-----+
| 1 | A | 1 |
| 1 | B | 2 |
| 1 | C | 3 |
| 2 | D | 1 |
| 2 | E | 2 |
| 2 | F | 3 |
| 3 | G | 1 |
| 3 | H | 2 |
| 3 | I | 3 |
+-------+------+-----+
To learn how to create the sets, have a look at this question/answer.
Then its a simple
ORDER BY tmp, group, name
回答2:
I'd try something like:
SET @counter = 0;
SELECT (@counter:=@counter+1)%3 as rr, grp, name FROM table ORDER by rr, grp
回答3:
You can use MySQL variables to do this.
SELECT grp, name, @row:=@row+1 from table, (SELECT @row:=0) r ORDER BY (@row % 3);
+------+------+--------------+
| grp | name | @row:=@row+1 |
+------+------+--------------+
| 1 | A | 1 |
| 2 | D | 4 |
| 3 | G | 7 |
| 1 | B | 2 |
| 2 | E | 5 |
| 3 | H | 8 |
| 1 | C | 3 |
| 2 | F | 6 |
| 3 | I | 9 |
+------+------+--------------+
来源：https://stackoverflow.com/questions/631259/is-there-a-way-in-sql-mysql-to-do-a-round-robin-order-by-on-a-particular-fie