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单选题
关系模式Sailors(sid,lastname.firtname,age,ratring)其中lastname允许为空. 下面哪个语句能够查找出lastname属性值不为空的水手信息.
A
SELECT * FROM SAILORS WHERE LASTNAME<>＇NULL＇
B
SELECT * FROM SAILORS WHERE LASTNAME<>NULL
C
SELECT * FROM SAILORS WHERE LASTNAME IS not NULL
D
SELECT * FROM SAILORS WHERE LASTNAME not LIKE ＇NULL＇
答案解析
正确答案：C
