The logical sum of negatives in the WHERE clause?

Table definitions and contents

CREATE TABLEER
    (`id`int,`age`int)
;

INSERT INTER
    (`id`,`age`)
VALUES
    (1, 1),
    (2, 2),
    (3, 5),
    (4, 7),
    (5, 9)
;

Results you want to extract
did is not 3 < or 」age is not 2 では record

1,1
4,7
5,9

SQL1Tried
The result was unintended.
What does the following mean?

SELECT* FROM`r`WHERE`id`!=3 OR`age`!=2;

SQL2Tried
I was able to get the intended result (even though it's AND). Why?
Is this the logical sum of negatives?

SELECT* FROM`r`WHERE`id`!=3AND`age`!=2;

mysql

2022-09-30 16:50

1 Answers

SQL1 is the negative OR (NOR) and SQL2 is the negative OR (NAND).

I think it's easy to understand if you think about it as a reverse event.
SQL1 is the inverse of id=3ANDage=2(A BB), so id!=3ORage!=2(notA nnotB).
In other words, it's the opposite of the combination of (3,2), so I'll select something other than the combination of (3,2).

SQL2 is the inverse of id=3orage=2(A BB), so id!=3ANDage!=2(notA nnotB).
If id=3 or age=2 is selected (2,2)(3,5) and it is the opposite, so the rest will be returned.

Also, it may be easy to draw a Ben diagram of A and B and A or B, and vice versa.

2022-09-30 16:50

If you have any answers or tips

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