A.应尽量避免在WHERE子句中使用OR来连接条件
B.应尽量避免在WHERE子句中对字段进行函数操作。
C.尽量在多表关联查询时使用子查询。
D.对查询进行优化,应尽量避免全表扫描。
A.SELECT * FROM student where id=l,2,3:
B.SELECT * FROM student where (id=1, id=2, id=3)
C.SELECT * FROM student where id in (1,2,3)
D.SELECT * FROM student where id in 1,2,3
A.SELECT姓名FROMSWHEREEXISTS(SELECT*FROMSCWHERE学号=学号AND课程号='C2')
B.SELECT姓名FROMSWHERE学号IN(SELECT学号FROMSCWHERE课程号='C2')
C.SELECT姓名FROMSINNERJOINSCON学号=sc.学号WHERE课程号='C2'
D.SELECT姓名FROMSWHERE学号=(SELECT学号FROMSCWHERE课程号='C2)
A.select*fromt_studentorderbyscorelimit100
B.select*fromt_studentorderbyscore
C.selectname,scoreaspfromt_studentorderbyplimit100
D.selectname,scoreassfromt_studentorderbyscorelimit100