in the MySQL query, if you want to filter out specific records, generally using
= comparison operator, for example:
SELECT * FROM users WHERE name ''
but when the need to extract
name equal to NULL records, you cannot use the
SELECT * FROM users WHERE name = NULL
if the query is written so, find out anything, because in comparison with NULL basically has no meaning.
then query how to write
1) the first method
SELECT * FROM users WHERE name NULL
SELECT * FROM users WHERE name IS NULL
so the difference between
= is that
= can not be compared with the NULL,
but the above two methods, it is recommended to use the second, because the IS NULL (and IS NOT NULL) is a part of the ANSI standard, so it can also be used in other database.
<=> can only use.