Mysql各种查询快速复习

快速复习视频地址：https://www.bilibili.com/video/BV1Vt411z7wy?p=10

快速复习手册地址：https://www.runoob.com/mysql/mysql-insert-query.html

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 select * from xhrs_user_list

SELECT * from xhrs_user_list WHERE user_name='xhrs;

UPDATE xhrs_user_list SET user_name="ones" WHERE id=1

DELETE FROM xhrs_user_list  WHERE runoob_id=3

SELECT id, user_name, create_time FROM xhrs_user_list  WHERE user_name    LIKE    "%one"

SELECT country FROM Websites UNION  SELECT country FROM appsa ORDER BY country  取得交集也就是，只有不同的值才显示

SELECT country FROM Websites UNION ALL SELECT country FROM appsa ORDER BY country  不管是否有交集，都显示，既显示所有结果值

SELECT * FROM xhrs_user_list  ORDER BY create_time; 默认情况下，它是按升序排列

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在分组的列上我们可以使用 COUNT, SUM, AVG,等函数。

SELECT user_name COUNT(*)  FROM  xhrs_user_list  GROUP BY user_name;  显示user_name通过 user_name分组查询

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INNER JOIN

SELECT a.user_id, a.user_author, b.user_count FROM class_tbl a INNER JOIN class_tbl b ON a.user__author = b.class_author