sql 使用记录

1.sql 查询某个属性值等于A 或 B 或者 C

select * from xx where x in （‘A’，‘B’，‘C’）

2.在联合查询时两个数据库表的属性列有相同 可以通过as 将其转换名称

select A.ID as ai ,B.ID as bi

from A , B

where .......

3.连接查询问题

有四个数据表

z_w_Record ，z_w_Door，z_w_User ，z_w_Class

对记录的查询 如果门名称不存在 或者用户名称不存在或者部门名称不存在 则显示null操作如下：

select u.z_CardNumber as uc ,r.z_CardNumber as rc ,u.z_UserName,d.z_ControllerDoorName,c.z_DepartmentClass,r.z_ReadDate,r.z_Event
from (z_w_Record as r left join z_w_Door as d on d.z_DoorID = r.z_DoorID) left join ( z_w_User as u left join z_w_Class as c on u.z_ClassID = c.z_ClassID ) on u.z_CardNumberHex = r.z_CardNumber
where r.z_ReadDate between '%s' and '%s' order by r.z_ReadDate asc",m_BeginTime,m_EndTime