在sql中选择限制答案

【问题标题】：select limit in sql在sql中选择限制
【发布时间】：2020-05-24 08:32:28
【问题描述】：

我写了这个查询，但在第 15 行（限制子句）给了我一个错误。我们有 3 个表，状态、电子邮件和接收者。

CREATE PROCEDURE `inbox`(IN `page_size` INT,IN `page_number` INT)
BEGIN
    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 @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 @offset,page_size;
END

【问题讨论】：

标签： sql stored-procedures sql-order-by sql-limit

【解决方案1】：

MySQL 不支持LIMIT 子句中的用户变量。相反，您可以使用常规变量：

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//

【讨论】：