将 Firebird 存储过程转换为 MySQL

Question

我在将存储过程从 Firebird 转换为 MySQL 时遇到了麻烦。

以下是 Firebird 的现有代码：

SET TERM ^ ;

CREATE OR ALTER PROCEDURE "ActPerHour" (
    days integer)
returns (
    "DateHour" varchar(32),
    "ActCount" integer)
as
declare variable "hours" integer;
declare variable "momentum" timestamp;
BEGIN
    select cast('NOW' as timestamp) from rdb$database into :"momentum";
    IF (:days > 31) THEN
    EXCEPTION "max_a_month";
    "hours" = :days*24;
    WHILE (:"hours" >= 0) DO
    BEGIN
        select substring(addhour (:"momentum", -:"hours") from 1 for 13),
               CASE
                   WHEN count(*) is NULL THEN 0
                   ELSE count(*)
                END
        from "Activity"
        where substring(timestamp '01/01/1970' + "started" / 86400.00000 from 1 for 13) = substring(addhour (:"momentum", -:"hours") from 1 for 13)
        and "started" > cast((:"momentum"-:days - timestamp '1970-01-01') * 86400 as integer)
        into :"DateHour", :"ActCount";
        "hours" = "hours" - 1;
        SUSPEND;
    END
END^

SET TERM ; ^

GRANT SELECT ON "Activity" TO PROCEDURE "ActPerHour";

GRANT EXECUTE ON PROCEDURE "ActPerHour" TO USER;

我在 MySQL 中尝试了以下操作：

DELIMITER $$
CREATE PROCEDURE ActPerHour (
    IN days INT,
    OUT DateHour VARCHAR(32),
    OUT ActCount INT)
BEGIN
    DECLARE hours INT;
    DECLARE momentum DATETIME;
SELECT NOW() INTO momentum;
    IF (days > 31) THEN
        BEGIN
            SELECT 'Maximum een maand' AS message;
        END;
    END IF;
    set hours = days * 24;
    WHILE (hours >= 0) DO
    BEGIN
        select (momentum - hours),
               CASE
                   WHEN count(*) is NULL THEN 0
                   ELSE count(*)
               END
        from result
        where started = (momentum - hours)
        and started > momentum - days
        into DateHour, ActCount;
        set hours = hours - 1;
    END;
END$$
DELIMITER ;

但我总是遇到 1064 错误。

错误代码：1064。您的 SQL 语法有错误；请查看与您的 MySQL 服务器版本相对应的手册，了解第 28 行“”附近使用的正确语法

我哪里错了？