MySQL—语法总结（2）子查询、连接、函数

比较运算符：=、>、<、>=、<=、<>、!=、<=>

SELECT AVG(col_name) FROM tb_name;                             # 对指定字段使用聚合函数
SELECT ROUND((AVG(col_name),2) FROM tb_name;                   # 对聚合函数结果保留两位小数
SELECT col_name1,col_name2 FROM tb_name WHERE col_name1 >(SELECT ROUND((AVG(col_name),2) FROM tb_name) ;        # 子查询作为外层查询的条件

SELECT...FROM...WHERE col_name > [ANY|SOME|ALL](...)                      # ANY、SOME、ALL关键字