1.sql 查詢某個屬性值等於A 或 B 或者 C
select * from xx where x in (‘A’,‘B’,‘C’)
2.在聯合查詢時兩個數據庫表的屬性列有相同 可以通過as 將其轉換名稱
select A.ID as ai ,B.ID as bi
from A , B
where .......
3.連接查詢問題
有四個數據表
z_w_Record ,z_w_Door,z_w_User ,z_w_Class
對記錄的查詢 如果門名稱不存在 或者用戶名稱不存在或者部門名稱不存在 則顯示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