B、select firstname+’.’+lastname=’name’ from employee
C、select ’name’=firstname+’.’+lastname from employee
D、select firstname,lastname from employee
B、select firstname+’.’+lastname=’name’ from employee
C、select ’name’=firstname+’.’+lastname from employee
D、select firstname,lastname from employee
A. select firstname+’.’+lastnameas’name’from employee
B. select firstname+’.’+lastname=’name’from employee
C. select’name’=firstname+’.’+lastnamefrom employee
D. select firstname,lastname from employee
B.此表设计主键时,根据选择主键的最小性原则,最好采用userid作为主键
C.此表设计主键时,根据选择主键的最小性原则,最好采用username和password作为组合键
D.如果采用userid作为主键,那么在userid列输入的数值,允许为空
A.selectstudent_id,sum(course_id)fromlearn
B.selectstudent_id,count(course_id)fromlearngroupbystudent_id
C.selectstudent_id,count(course_id)fromlearn
D.selectstudent_id,sum(course_id)fromlearngroupbystudent_id
B、select sum(*) from student_tb where sex = '男';
C、select avg(*) from student_tb where sex = '男';
D、select max(*) from student_tb where sex = '男';
A、update students set Grade=Grade+10 where SID=1
B、update * set Grade=Grade+10
C、update * from stedents set Grade=Grade+10
D、update students set Grade=Grade+10
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