SQL查詢語句,多表的連接
1、兩個表的連接:
select distinct scourseName from tbStuSelect where stuRName in (select stuRealName from tbStudentInfo where stuID=12)
select courseID,courseName,courseTeaI,courseDate,teaID,teaRealName from tbCourseInfo,tbTeacherInfo where courseTeaID=teaID
2、三個表的連接:通過inner join 可以去掉重複的列,在實現搜索功能時很有用
select shwID,hwteahwID,hwPath,hwSubmitTime,hwUploadStatus,hwTitle,hwcourseName,hwEndTime,teaRealName from tbStuHomeworkInfo inner join tbTeaHomeworkInfo on hwteahwID=hwID inner join tbTeacherInfo on teaID=hwteaID
3、去掉重複的內容
select distinct courseName from tbCourseInfo
4、sql語句,比較時間,找出時間比今天早的列
select * from tbTeaHomeworkInfo where datediff(day,hwEndTime,getdate())<0
寫程序時,最好需要什麼數據,就查找什麼數據。不需要老是全部查詢。
有其他的,再繼續總結。