http://dev.mysql.com/doc/refman/5.7/en/comparison-operators.html#function_in

SELECT val1 FROM tbl1 WHERE val1 IN (1,2,'a');


The number of values in the ​​IN​​ list is only limited by the ​​max_allowed_packet​​ value.

 

http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_allowed_packet

You must increase this value if you are using large ​​BLOB​​ columns or long strings. It should be as big as the largest ​​BLOB​​ you want to use. The protocol limit for ​​max_allowed_packet​​ is 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.