Syntax:
expr IN (value,...)

Returns 1 (true) if expr is equal to any of the values in the IN()
list, else returns 0 (false).

Type conversion takes place according to the rules described in
https://dev.mysql.com/doc/refman/5.7/en/type-conversion.html, applied
to all the arguments. If no type conversion is needed for the values in
the IN() list, they are all constants of the same type, and expr can be
compared to each of them as a value of the same type (possibly after
type conversion), an optimization takes place. The values the list are
sorted and the search for expr is done using a binary search, which
makes the IN() operation very quick.

URL: https://dev.mysql.com/doc/refman/5.7/en/comparison-operators.html

