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    Enter password: ******
    Welcome to the MySQL monitor. Commands end with ; or g.
    Your MySQL connection id is 11
    Server version: 5.1.55-community MySQL Community Server (GPL)

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    and you are welcome to modify and redistribute it under the GPL v2 license

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    mysql> use test_1
    Database changed
    mysql> select * from student;
    ERROR 1146 (42S02): Table 'test_1.student' doesn't exist
    mysql> select * from students;
    +--------+----------+---------+
    | stu_id | stu_name | stu_sex |
    +--------+----------+---------+
    | 1 | xiaobai | F |
    +--------+----------+---------+
    1 row in set (0.01 sec)

    mysql> select * from students;
    +--------+----------+---------+
    | stu_id | stu_name | stu_sex |
    +--------+----------+---------+
    | 1 | xiaobai | F |
    | 2 | xiaobai | F |
    | 3 | xiaobai | F |
    | 4 | xiao | F |
    | 5 | xiaoming | F |
    +--------+----------+---------+
    5 rows in set (0.00 sec)

    mysql> select stu_id, stu_name, stu_sex from students group by stu_name;
    +--------+----------+---------+
    | stu_id | stu_name | stu_sex |
    +--------+----------+---------+
    | 4 | xiao | F |
    | 1 | xiaobai | F |
    | 5 | xiaoming | F |
    +--------+----------+---------+
    3 rows in set (0.01 sec)

    mysql> select distinct stu_name from students;
    +----------+
    | stu_name |
    +----------+
    | xiaobai |
    | xiao |
    | xiaoming |
    +----------+
    3 rows in set (0.00 sec)

    mysql> select distinct stu_name, stu_id, stu_sex from students;
    +----------+--------+---------+
    | stu_name | stu_id | stu_sex |
    +----------+--------+---------+
    | xiaobai | 1 | F |
    | xiaobai | 2 | F |
    | xiaobai | 3 | F |
    | xiao | 4 | F |
    | xiaoming | 5 | F |
    +----------+--------+---------+
    5 rows in set (0.00 sec)

    mysql> select *, count(distinct stu_name) from students group by stu_name;
    +--------+----------+---------+--------------------------+
    | stu_id | stu_name | stu_sex | count(distinct stu_name) |
    +--------+----------+---------+--------------------------+
    | 4 | xiao | F | 1 |
    | 1 | xiaobai | F | 1 |
    | 5 | xiaoming | F | 1 |
    +--------+----------+---------+--------------------------+
    3 rows in set (0.01 sec)

    mysql>

    目的:从表中筛选出不重复的

    1.从表中仅仅将某一列的不重复项给筛选出来
    select distinct stu_name from students;
    仅仅将students表中stu_name列里不重复的项给筛选出来

    2.从表中将某一列的不重复项给筛选出来,同时其关联的其它列也一起显示出来
    select stu_id, stu_name, stu_sex from students group by stu_name;
    使用的是group by
    note:重复项保留的是最先出现的那一行

    3.select *, count(distinct stu_name) from students group by stu_name;
    会在输出的地方添加count(distinct stu_name)列

    4.select distinct stu_name, stu_id, stu_sex from students;
    会改变列的列号

    5.select *, count(distinct stu_name) from students;

    mysql> select *, count(distinct stu_name) from students;
    +--------+----------+---------+--------------------------+
    | stu_id | stu_name | stu_sex | count(distinct stu_name) |
    +--------+----------+---------+--------------------------+
    | 1 | xiaobai | F | 3 |
    +--------+----------+---------+--------------------------+
    1 row in set (0.00 sec)

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  • 原文地址:https://www.cnblogs.com/qbin/p/10041523.html
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