Basic SQL logic of NOT and NULL values when using =
select * from dual where not (1=2 );
One row returned.
select * from dual where not ( 5=null);
No rows returned.
select * from dual where not (1=2 and 5=null);
Unexpectedly, row returned.
Am I missing something basic how NOT works?
Or how AND works?
Tried in Oracle 11 and 12.
sql oracle
asked Nov 13 '18 at 22:07
goo54321goo54321
63
add a comment |
select * from dual where not (1=2 );
One row returned.
select * from dual where not ( 5=null);
No rows returned.
select * from dual where not (1=2 and 5=null);
Unexpectedly, row returned.
Am I missing something basic how NOT works?
Or how AND works?
Tried in Oracle 11 and 12.
sql oracle
asked Nov 13 '18 at 22:07
goo54321goo54321
63
add a comment |
select * from dual where not (1=2 );
One row returned.
select * from dual where not ( 5=null);
No rows returned.
select * from dual where not (1=2 and 5=null);
Unexpectedly, row returned.
Am I missing something basic how NOT works?
Or how AND works?
Tried in Oracle 11 and 12.
sql oracle
asked Nov 13 '18 at 22:07
goo54321goo54321
63
select * from dual where not (1=2 );
One row returned.
select * from dual where not ( 5=null);
No rows returned.
select * from dual where not (1=2 and 5=null);
Unexpectedly, row returned.
Am I missing something basic how NOT works?
Or how AND works?
Tried in Oracle 11 and 12.
sql oracle
sql oracle
asked Nov 13 '18 at 22:07
goo54321goo54321
63
asked Nov 13 '18 at 22:07
goo54321goo54321
63
asked Nov 13 '18 at 22:07
goo54321goo54321
63
asked Nov 13 '18 at 22:07
goo54321goo54321
63
asked Nov 13 '18 at 22:07
goo54321goo54321
63
63
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
This is all fine. Almost any operation with NULL returns NULL, including =, <>, and NOT.
But, let's parse that last where:
where not (1 = 2 and 5 = null);
is the same as:
where not (FALSE and NULL)
Well, AND returns FALSE if any of the operands are FALSE -- even if others are NULL. Look at this another way, whether the NULL is "TRUE" or "FALSE", the expression is FALSE.
Hence, the result is the same as:
where TRUE
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
@user2469062 . . .NULL OR FALSEreturnsNULL, butNULL AND FALSEis well-defined, because of theFALSE.
– Gordon Linoff
Nov 13 '18 at 22:34
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
add a comment |
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1 Answer
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1 Answer
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This is all fine. Almost any operation with NULL returns NULL, including =, <>, and NOT.
But, let's parse that last where:
where not (1 = 2 and 5 = null);
is the same as:
where not (FALSE and NULL)
Well, AND returns FALSE if any of the operands are FALSE -- even if others are NULL. Look at this another way, whether the NULL is "TRUE" or "FALSE", the expression is FALSE.
Hence, the result is the same as:
where TRUE
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
@user2469062 . . .NULL OR FALSEreturnsNULL, butNULL AND FALSEis well-defined, because of theFALSE.
– Gordon Linoff
Nov 13 '18 at 22:34
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
add a comment |
This is all fine. Almost any operation with NULL returns NULL, including =, <>, and NOT.
But, let's parse that last where:
where not (1 = 2 and 5 = null);
is the same as:
where not (FALSE and NULL)
Well, AND returns FALSE if any of the operands are FALSE -- even if others are NULL. Look at this another way, whether the NULL is "TRUE" or "FALSE", the expression is FALSE.
Hence, the result is the same as:
where TRUE
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
@user2469062 . . .NULL OR FALSEreturnsNULL, butNULL AND FALSEis well-defined, because of theFALSE.
– Gordon Linoff
Nov 13 '18 at 22:34
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
add a comment |
This is all fine. Almost any operation with NULL returns NULL, including =, <>, and NOT.
But, let's parse that last where:
where not (1 = 2 and 5 = null);
is the same as:
where not (FALSE and NULL)
Well, AND returns FALSE if any of the operands are FALSE -- even if others are NULL. Look at this another way, whether the NULL is "TRUE" or "FALSE", the expression is FALSE.
Hence, the result is the same as:
where TRUE
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
This is all fine. Almost any operation with NULL returns NULL, including =, <>, and NOT.
But, let's parse that last where:
where not (1 = 2 and 5 = null);
is the same as:
where not (FALSE and NULL)
Well, AND returns FALSE if any of the operands are FALSE -- even if others are NULL. Look at this another way, whether the NULL is "TRUE" or "FALSE", the expression is FALSE.
Hence, the result is the same as:
where TRUE
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
answered Nov 13 '18 at 22:10
Gordon LinoffGordon Linoff
766k35300402
766k35300402
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
@user2469062 . . .NULL OR FALSEreturnsNULL, butNULL AND FALSEis well-defined, because of theFALSE.
– Gordon Linoff
Nov 13 '18 at 22:34
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
add a comment |
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
@user2469062 . . .NULL OR FALSEreturnsNULL, butNULL AND FALSEis well-defined, because of theFALSE.
– Gordon Linoff
Nov 13 '18 at 22:34
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
Thanks for the explanation. I guess my assumption was NULL and FALSE, would return NULL.
– goo54321
Nov 13 '18 at 22:23
@user2469062 . . .
NULL OR FALSE returns NULL, but NULL AND FALSE is well-defined, because of the FALSE.– Gordon Linoff
Nov 13 '18 at 22:34
@user2469062 . . .
NULL OR FALSE returns NULL, but NULL AND FALSE is well-defined, because of the FALSE.– Gordon Linoff
Nov 13 '18 at 22:34
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
I thought this was an interesting little topic so I made an SQLFiddle to show what's legitimate and what isn't. I thought others might find it informative.
– Bob Jarvis
Nov 13 '18 at 23:16
add a comment |
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