Syntax:
value MEMBER OF(json_array)

Returns true (1) if value is an element of json_array, otherwise
returns false (0). value must be a scalar or a JSON document; if it is
a scalar, the operator attempts to treat it as an element of a JSON
array.

Queries using MEMBER OF() on JSON columns of InnoDB tables in the WHERE
clause can be optimized using multi-valued indexes. See
https://dev.mysql.com/doc/refman/8.0/en/create-index.html#create-index-
multi-valued, for detailed information and examples.

URL: https://dev.mysql.com/doc/refman/8.0/en/json-search-functions.html

