On 3/6/20 9:00 PM, Simon Slavin wrote:
On 7 Mar 2020, at 1:52am, Xinyue Chen <chenx...@uw.edu> wrote:
If I change IS NOT FALSE to IS TRUE, the results will be different. I
assume they should perform in the same way?
No. Because NULL is not TRUE and is not FALSE.
SQLite version 3.28.0 2019-04-15 14:49:49
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> SELECT NULL IS TRUE;
0
sqlite> SELECT NULL IS FALSE;
0
sqlite> SELECT NULL IS NOT TRUE;
1
sqlite> SELECT NULL IS NOT FALSE;
1
Once you can have NULL values, you have to know the rules very well when you
apply logic. Other values make sense, but NULL is not logical.
It is sort of like NaN, where a Nan is neither less than, greater than
or equal to any value, including itself.
--
Richard Damon
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