Category Archives: Mysql

把某字段第10位设置为1

update tests set uid = uid|(1 << 10) where id=1;

把某个字段第10位设置为0

update tests set uid = uid&~(1 << 10) where id=1;

CREATE DATABASE IF NOT EXISTS 数据库名字 DEFAULT CHARACTER SET utf8mb4 DEFAULT COLLATE utf8mb4_general_ci;

SELECT @rowNum:=@rowNum + 1 AS ‘行号’,a.* FROM Teacher a,(SELECT @rowNum:=0) b;

DELETE p from a p inner JOIN b i on p.id=i.pic_id  where ……;

where条件之后随便写

1、使用not in，容易理解，效率低

select distinct A.ID from A where A.ID not in (select ID from B)

2、使用left join…on… ，B.ID isnull表示左连接之后在B.ID字段为null的记录

select A.ID from A left join B on A.ID=B.ID where B.ID is null