13

我有一个有两列的表。

+------+------+
| data | num  | 
+------+------+
| a    |      | 
| a    |      |
| a    |      |
| b    |      |
| b    |      |
| c    |      |
| d    |      |
| a    |      |
| b    |      | 
+------+------+

我希望“num”列为每个重复条目显示一个增量计数器：

+------+------+
| data | num  | 
+------+------+
| a    |    1 | 
| a    |    2 |
| a    |    3 |
| b    |    1 |
| b    |    2 |
| c    |    1 |
| d    |    1 |
| a    |    4 |
| b    |    3 | 
+------+------+

除了 mySQL 查询之外，这是否可以在没有任何其他脚本的情况下完成？

更新：

扩展问题在这里

4

4 回答 4

14

不幸的是，MySQL 没有您需要的窗口函数。所以你将不得不使用这样的东西：

最终查询

select data, group_row_number, overall_row_num
from
(
  select data,
        @num := if(@data = `data`, @num + 1, 1) as group_row_number,
        @data := `data` as dummy, overall_row_num
  from
  (
    select data, @rn:=@rn+1 overall_row_num
    from yourtable, (SELECT @rn:=0) r
  ) x
  order by data, overall_row_num
) x
order by overall_row_num

见SQL Fiddle with Demo

解释：

首先，内部选择，这将模拟应用于row_number表中的所有记录（参见SQL Fiddle with Demo）：

select data, @rn:=@rn+1 overall_row_num
from yourtable, (SELECT @rn:=0) r

查询的第二部分，将表中的每一行与下一行进行比较，看它是否具有相同的值，如果没有，则重新开始group_row_number（参见SQL Fiddle with Demo）：

select data,
      @num := if(@data = `data`, @num + 1, 1) as group_row_number,
      @data := `data` as dummy, overall_row_num
from
(
  select data, @rn:=@rn+1 overall_row_num
  from yourtable, (SELECT @rn:=0) r
) x
order by data, overall_row_num

最后一个选择，返回您想要的值并将它们按您请求的顺序放回：

select data, group_row_number, overall_row_num
from
(
  select data,
        @num := if(@data = `data`, @num + 1, 1) as group_row_number,
        @data := `data` as dummy, overall_row_num
  from
  (
    select data, @rn:=@rn+1 overall_row_num
    from yourtable, (SELECT @rn:=0) r
  ) x
  order by data, overall_row_num
) x
order by overall_row_num
于 2012-09-17T17:08:56.877 回答
4

这是一个简单的查询，可以满足您的要求。

select id,data,rownum 
  from (
          select id,
                 data,
                 @row:=if(@prev=data,@row,0) + 1 as rownum,
                 @prev:=data 
            from tbl
        order by data,id
)t

我在每一行都包含了一个 id。但你不需要它。

去小提琴：http ://sqlfiddle.com/#!2/1d1f3/11/0

信用： 想要 MY SQL 中列组的行号？

于 2012-09-17T17:21:31.903 回答
0

数据是否必须保持显示的顺序，或者我们可以按“数据”值排序？

如果您可以排序，那么您只需要跟踪当前的“数据”值，这可以通过变量来完成：

set @last_data = null;
set @count = 0;
select data, @count,
  case when @last_data is null or data != @last_data then @count := 1 else @count := @count + 1 end as new_count,
  @last_data := data, @count
from t20120917
order by data;

如果没有，我认为它会更复杂......

于 2012-09-17T17:08:20.223 回答
0

它是这样的，但你需要创建程序

create procedure procname()
begin
DECLARE done,i,j int DEFAULT 0;
DECLARE n,m nvarchar(500) DEFAULT '';

DECLARE cur CURSOR FOR SELECT d.data,d.num FROM tablename AS d ORDER BY DATA;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;


OPEN cur;

read_loop: LOOP

set m = n;
SET j = i;
fetch cur into n,i;

IF n = m 
THEN
SET i = i+1;
// UPDATE here your TABLE but you will need one more colomn to be able to UPDATE ONLY one RAW that you need
ELSE 
SET i = 0; //RESET indexer 
END IF;

IF done = 1 THEN
LEAVE read_loop;
END IF;

END LOOP read_loop;

CLOSE cur;
end
于 2012-09-17T17:12:14.603 回答