mysql - 自定义行编号

Question

我希望在从表中选择时对数据行进行编号。问题是，我不需要顺序编号，但它应该从 1 到 3 依次编号到最后，如下所示:

1 | first row
2 | second row
3 | third row 
1 | fourth row
2 | and
3 | ....
1
2
3

我正在尝试这个查询，但它不能正常工作:

mysql -> SET @n = 0;
-> SELECT 
CASE 
    WHEN nnn = 3 THEN  @n := 0
        ELSE nnn
    END
FROM  (
    SELECT @n := @n + 1 AS nnn FROM mytable
) AS t;

如何让它正常工作？

Answer 1

改编自此答案:With MySQL, how can I generate a column containing the record index in a table?

SELECT  MOD(@curRow := @curRow + 1, 3) AS row_number
FROM    mytable m
JOIN    (SELECT @curRow := 0) r;