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not null query returning null value

Posted on 2015-01-28
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Last Modified: 2015-01-29
hi i have the folloing query but returning null value even if there is no value related to other table

SELECT * FROM CAL_OBJ
          WHERE TRIM(OBJ_NAME) NOT IN(SELECT TRIM(OBJ_NAME) FROM cal_book);this query return null
        
 
          select * from cal_book
          where obj_name = 'LHLODS06.FMB';this query return null
          
           select * from cal_obj
          where obj_name = 'LHLODS06.FMB';  this query return value

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THE second query suppose to be the one to return value not the last query, is there another way to write the first query
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Question by:chalie001
7 Comments
 
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Expert Comment

by:Olaf Doschke
ID: 40576803
In case of the second query, what do you mean it returns NULL? You query whole records. If there is no cal_book with the obj_name 'LHLODS06.FMB', you get no records, an empty result set, but not NULL.

If you get an empty result set a NOT IN subquery can't check a value against a set of other values and therefore this also results in an empty result set.

You should rather use NOT EXISTS.

Bye, Olaf.
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LVL 28

Expert Comment

by:Naveen Kumar
ID: 40576823
Does your obj_name column in cal_obj has null values  ?

check with this :

select * from cal_obj
          where obj_name is null ?
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Author Comment

by:chalie001
ID: 40576903
i whated to say it return blank no value at all
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Expert Comment

by:Naveen Kumar
ID: 40576912
do you mean that query returned 0 records ? do not confuse with words blank, no value, null etc
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Accepted Solution

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Naveen Kumar earned 2000 total points
ID: 40576921
you should use this query to get all form names which exist in the cal_obj table but not in the cal_book table.

  select * from cal_obj a
          where not exists ( select 1 from cal_book b where a.obj_name = b.obj_name );

Test it out.

Thanks,
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LVL 35

Expert Comment

by:Mark Geerlings
ID: 40578068
"I wanted to say it return blank no value at all"  That is not the same as returning a null.

Try this example:

create table test_tab
(item_code    varchar2(3),
 price        number(6,2),
 date_shipped date);
 
insert into test_tab
values ('ABC',15, trunc(sysdate - 1));

insert into test_tab
values ('DEF',25, trunc(sysdate));
 
insert into test_tab
values ('GHI',30, null);

commit;

If you run either of these queries:
select * from  test_tab;
or
select * from  test_tab where item_code = 'GHI';

You *WILL* get  a null value returned for column: "date_shipped" in the record for 'GHI'.

If you run this query:
select * from  test_tab where item_code = 'XYZ';

You will get no rows returned.  That is different from "returning a null".
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Author Closing Comment

by:chalie001
ID: 40578140
thanks
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