MySQL:排除重复数据 [英] MySQL: Exclude duplicate data

问题描述

在我的一列中，有重复项，我只想抓住第一次出现的情况.我怎样才能做到这一点?在示例中，我想获取col C中唯一的所有行.因此，我只想要hello ladies，hello team，hello cats和hello sexy

In one of my columns, there's are duplicates and I want to grab the first occurrence only. How can I do that? In the example, I want to grab all the rows that are unique in col C. So I only want hello ladies, hello team, hello cats, and hello sexy

Example Table
---------------

column A | col B | col C 
--------------------------
hello    | ladies| 1
hello    | guys  | 1
hello    | team  | 2
hello    | dogs  | 2
hello    | cats  | 3
hello    | cats  | 3
hello    | sexy  | 4

推荐答案

DISTINCT 关键字不适用于您的情况.

The DISTINCT keyword is not applicable in your case.

在DB中，行的顺序是任意的.但是，您可以使用可与字符串一起使用的聚合函数，为每个唯一C值仅选择B列之一.如果字符串的最大值"， MAX 就是这样的函数是可以接受的选择:

In the DB the order of rows is arbitrary. You can however select just one of the B column for each unique C value using an aggregate function that can work with strings. MAX is such a function, if the 'maximum' of strings is an acceptable choice:

mysql> select A,max(B),C from Test group by C,A;
+-------+--------+------+
| A     | max(B) | C    |
+-------+--------+------+
| hello | ladies |    1 |
| hello | team   |    2 |
| hello | cats   |    3 |
| hello | sexy   |    4 |
+-------+--------+------+
4 rows in set (0.00 sec)

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