MySQL syntax error 1064 near IN stored procedure
MemSQL is not MySQL - see e.g. their page MySQL Features Unsupported in MemSQL. For details on their stored procedure implementation, please refer to MemSQL's documentation on stored procedures:

[USING database_name] CREATE [OR REPLACE] PROCEDURE procedure_name ( [parameter_list] )
  [RETURNS { data_type [data_type_modifier] } ] AS
  [DECLARE variable_list] [ ...n ]
  BEGIN
    procedure_body
  END ;

parameter_list:
  parameter_name data_type [data_type_modifier [ ...n ] ] [, ...]

data_type_modifier:
  DEFAULT default_value | NOT NULL | NULL | COLLATE collation_name

variable_list:
  variable_name type_expression [= value_expression ] ; [... ;]


As you can see, there is apparently no support for declaring parameters as IN, OUT, or INOUT. (They do however support default values for parameters, something which neither MySQL nor MariaDB support!)