Is there any reason to use = instead of <=> in MariaDB/MySQL? It seems that the = operator is only desirable if the null is desirable for result of the expression.
Are there any consequences of replacing every = with <=>? Even if both operands can never be null (for which the behaviour should remain the exact same)?
First of all, the meaning of NULL is quite unclear. There are many articles in the Internet about how people interpret it.
Therefore, using <=> could just add to the confusion and you risk than other developers may not understand it well. It strongly deviates from the standard behavior most people expect from queries. I would suggest you avoid it unless there are strong reasons why to use it.
IS DISTINCT FROM that does the same.
a = b -- Always NULL (which is usually treated as False) if either is NULL a <=> b -- True if _both_ are NULL If both columns are declared NOT NULL, there is no use to use <=>.
In almost all other cases, your logic is not going to care.
I almost never see anyone using <=>.
NULLas no value, its meaning in equality operations is a little odd, however there are cases where<=>make sense. SomeJOINs will be have rather differently with<=>rather than=. I'd keep to using<=>as an exceptional case rather than the default.