mysql不支持中的用户变量 LIMIT 条款。相反，可以使用正则变量：

DELIMITER //

CREATE PROCEDURE `inbox`(IN `page_size` INT,IN `page_number` INT)
BEGIN
    DECLARE v_offset INT;
    SET @curr = ( SELECT entered_accounts.username
                FROM entered_accounts
                WHERE entered_accounts.time = (SELECT Max(entered_accounts.time) FROM entered_accounts));
    SET @tmp = page_number-1;
    SET v_offset = page_size * @tmp;

    SELECT email.subject, email.body, email.time, state.readed, state.deleted
    FROM email INNER JOIN reciever USING(email_id) 
                INNER JOIN state USING (email_id) 
    WHERE state.username=reciever.username AND LOWER(reciever.username)=LOWER(@curr) AND NOT reciever.username=email.username
    ORDER BY email.time DESC
    LIMIT v_offset, page_size;
END//