Oracle的BLOB空值

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Create table b(id varchar,obj blob);
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Insert into b(id) values(“A”);
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Insert into b(id,obj) values(“B”,empty_blob());
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Insert into b(id,obj) values(“C”,’’);
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Insert into b(id,obj) values(“D”,null);
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Select id,obj from b;
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   id     obj     length
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-----------------------------------------
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   A      0x        0
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   B      0x        0
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   C      0x        0
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   D      NULL     NULL