Unknown values and NULL
Comparison operators
NULL comparison operators
jao# select name from birthday where birth_date = NULL;
name
------
(0 rows)
jao# select name from birthday where birth_date != NULL;
name
------
(0 rows)
jao# select name from birthday where birth_date is NULL;
name
-------------------
Genghis Khan
Pope Boniface III
(2 rows)
jao# select name from birthday where birth_date is not NULL;
name
-----------------
Richard Feynman
Donald Knuth
(2 rows)
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