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  • MySQL 子查询与连接操作笔记

      SQL语句之间是可以进行连接操作的,在一些复杂的数据操作中必须用到连接操作。简单的说就是一个SQL语句的结果可以作为相连接的SQL操作的一部分。SQL结构化查询语句,子查询是指的所有的SQL操作,并非单一的SELECT语句。

        1.由比较运算符产生:

    SELECT user_name,user_id,user_phone FROM users WHERE user_age >=(SELECT ROUND(AVG(age),0) FROM users);

    可以使用ANY,SOME,ALL对查询进行。

    SELECT user_name,user_id,user_phone FROM users WHERE user_age >= ANY (SELECT ROUND(AVG(age),0) FROM users);

      2.由[NOT] IN/EXIS产生   

      

    SELECT user_name,user_id,user_phone FROM users WHERE user_age >= NOT IN (SELECT ROUND(AVG(age),0) FROM users);

      

      3.由INSERT......SELECT产生

    CREATE TABLE tdb_goods_brands (
    
        brand_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    
        brand_name VARCHAR(40) NOT NULL
    
      ) SELECT brand_name FROM tdb_goods GROUP BY brand_name
    UPDATE tdb_goods  INNER JOIN tdb_goods_brands ON brand_name = brand_name SET brand_name = brand_id;
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  • 原文地址:https://www.cnblogs.com/daiyu/p/4705438.html
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