查询出EMP表中COMM字段为空的记录（）A.select * from emp where comm=;B.select * from emp where comm=null;C.select * from emp where nvl(comm)=0;D.select * from emp where comm is null;E.select * from emp where nvl(comm,0)=0;

单项选择题

查询出EMP表中COMM字段为空的记录（）

A.select * from emp where comm='';
B.select * from emp where comm=null;
C.select * from emp where nvl(comm)=0;
D.select * from emp where comm is null;
E.select * from emp where nvl(comm,0)=0;

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