仅从一列中删除重复项答案

【问题标题】：Removing duplicates from one column only仅从一列中删除重复项
【发布时间】：2016-06-04 19:48:35
【问题描述】：

所以我会有这样的东西。它的结果是查询到两个表。

+------------------+------------------------------------+
| character_name   | title                              |
+------------------+------------------------------------+
| derp             | a                                  |
| derp             | b                                  |
| derp             | c                                  | 
| herp             | a                                  |
| herp             | b                                  |
| herp             | c                                  |
+-------------------------------------------------------+

我想要这个

+------------------+------------------------------------+
| character_name   | title                              |
+------------------+------------------------------------+
| derp             | a                                  |
|                  | b                                  |
|                  | c                                  | 
| herp             | a                                  |
|                  | b                                  |
|                  | c                                  |
+-------------------------------------------------------+

这可能吗？

【问题讨论】：

你可以在这里参考我的答案 ==> stackoverflow.com/questions/35125619/…
我猜你是想说：当显示时删除重复项
我只想删除 character_name 列的重复项。
点击链接，这将对您有所帮助。 stackoverflow.com/questions/17507887/…
stackoverflow.com/questions/17507887/… 点击链接，这将对您有所帮助。 stackoverflow.com/questions/28694871/…

标签： mysql sql database

【解决方案1】：

这是你的意思吗？

select case when i.rnk = 1 THEN i.character_name  ELSE '' END as NAME
, i.title
from(
    select *
    , row_number() over (partition by character_name order by title) as rnk
    from t1
) i
order by i.character_name

名字将获得值 1，您会在结果中显示该值，而您隐藏的任何其他内容。

更新 - MySql 版本：

SET @r_name:='';

select name, title FROM (
    select @r_name:=CASE WHEN @r_name = name THEN '' 
    ELSE name
    END AS name
    , @r_name:=name
    , title
    FROM
    t1
) t2

【讨论】：

这个查询是针对mysql的？！
@ashkufaraz 我没有注意标签，我已经添加了更新，谢谢。

【解决方案2】：

您可以在用户变量的帮助下完成。

SQL：

SET @last_name = '';
SELECT
    IF(switch_name, tbl2.character_name, '') character_name,
    tbl2.title
FROM
    (
    SELECT 
        character_name, 
        title, 
        character_name != @last_name switch_name, 
        @last_name:=character_name 
    FROM
        tbl
    ) tbl2;

结果：

mysql> SELECT character_name, title FROM tbl;
+----------------+-------+
| character_name | title |
+----------------+-------+
| derp           | a     |
| derp           | b     |
| derp           | c     |
| herp           | a     |
| herp           | b     |
| herp           | c     |
+----------------+-------+
6 rows in set (0.00 sec)

mysql> SET @last_name = '';
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> SELECT
    ->     IF(switch_name, tbl2.character_name, '') character_name,
    ->     tbl2.title
    -> FROM
    ->     (
    ->     SELECT
    ->         character_name,
    ->         title,
    ->         character_name != @last_name switch_name,
    ->         @last_name:=character_name
    ->     FROM
    ->         tbl
    ->     ) tbl2;
+----------------+-------+
| character_name | title |
+----------------+-------+
| derp           | a     |
|                | b     |
|                | c     |
| herp           | a     |
|                | b     |
|                | c     |
+----------------+-------+
6 rows in set (0.00 sec)

【讨论】：

【解决方案3】：

它将适用于您给定的表格

   SELECT CASE  
    WHEN character_name ='derp' AND title ='a' THEN 'derp'
    WHEN character_name ='derp' AND title ='b' THEN ''
    WHEN character_name ='derp' AND title ='c' THEN ''
    WHEN character_name ='herp' AND title ='a' THEN 'herp'
    WHEN character_name ='herp' AND title ='b' THEN ''
    WHEN character_name ='herp' AND title ='c' THEN ''
    end as character_name,
    title
    from table_name;

注意：如果您的数据是动态的或不是如上所示，那么您必须重写/优化查询以获得所需的结果。

【讨论】：