Question

我希望从表中选择时编号的数据行。问题是，我不需要顺序编号，但它应该从1到3编号，所以到最后，如下所示：

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

我正在尝试此查询，但它无法正常运行：

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

改编自这个答案：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;

Answer 2

如果你只需要选择并假设有一个列，比如说“id”，这是顺序的，那么下面的查询应该会有所帮助：

SELECT IF ((id%3) = 0, 3 , (id%3)) AS new_id, <other columns> FROM <table_name>;

希望它有所帮助...

自定义行编号

2 个答案: