题目内容

将计算机科学系全体学生的成绩置零，下列语句正确的有（）

A. UPDATE SC SET Grade=0 WHEREsno in (select sno from studentWHERE sdept = ‘CS’)
B. UPDATE SC SET Grade=0 WHERE(SELETE Sdept FROM StudentWHERE Student.Sno = SC.Sno)= 'CS'
C. UPDATE SC SET Grade=0 WHERE'CS'= (SELETE Sdept FROM StudentWHERE Student.Sno = SC.Sno)
D. UPDATE SC SET Grade=0 WHERE(SELETE Sdept FROM Student，SCWHERE Student.Sno = SC.Sno AND Sdept='CS')

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删除计算机科学系所有学生的选课记录,下列语句正确的为（）

A. DELETE FROM SC WHEREsno in (select sno from studentWHERE sdept = ‘CS’)
B. DELETE FROM SC WHERE(SELETE Sdept FROM StudentWHERE Student.Sno=SC.Sno) ='CS'
C. DELETE FROM SC WHERE 'CS'=(SELETE Sdept FROM StudentWHERE Student.Sno=SC.Sno)
DELETE FROM SC WHERE(SELETE Sdept FROM StudentWHERE Student.Sno=SC.Sno)

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DBMS在执行插入语句时会检查所插元组是否破坏表上已定义的完整性规则，如对于有NOT NULL约束的属性列是否提供了非空值，对于有UNIQUE约束的属性列是否提供了非重复值

A. 对
B. 错

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导热问题的第一类边界条件是已知

A. 壁温
B. 热流密度
C. 温度梯度
D. 温差

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下面哪种材料的导热系数最小

A. 铜
B. 金
C. 银
D. 硅藻土

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