mysql基础使用—— 判断空值，查询建表，[Err] 1055 以及随机取出记录

1. 判断是否是空值 is not null 和 is null

select * from XXX where column_name is not null;

select * from XXX where column_1 is not null and column_2 is not null;

2. [Err] 1055 - Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'information_schema.PROFILING.SEQ' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

原因：由 sql_mode 引起的。

SHOW VARIABLES LIKE '%sql_mode%';  或者 select version(), @@sql_mode; 都能看到sql_mode的value值是什么，可以见到它的值是：

ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

也就是存在：ONLY_FULL_GROUP_BY

解决方法：

执行：SET sql_mode=(SELECT REPLACE(@@sql_mode,'ONLY_FULL_GROUP_BY',''));

 3. 通过查询结果，创建新表

create table table_new select * from table_old where column_1='金庸';

4. 随机取出10条数据: order by rand()

select * from table where condition order by rand() limit 10;

参考：

https://www.cnblogs.com/acmexyz/p/10831536.html

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