MySQL 根据 DISTINCT 值对多行进行分组

Question

我需要显示表中的最后2个结果(结果)，结果由具有匹配submissionId的多行组成，每次提交的行数未知，当然我更喜欢单个查询。

这是数据库表结构

submissionId     input       value

     1           name         jay
     1           phone        123-4567
     1           email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="601405131420070d01090c4e030f0d" rel="noreferrer noopener nofollow">[email protected]</a> 
     2           name         mo
     2           age          32
     3           name         abe
     3           email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="7716151237101a161e1b5914181a" rel="noreferrer noopener nofollow">[email protected]</a>
     4           name         jack
     4           phone        123-4567
     4           email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="573d36343c17303a363e3b7934383a" rel="noreferrer noopener nofollow">[email protected]</a> 

期望的结果:

submissionId     input       value

     3           name         abe
     3           email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="18797a7d587f75797174367b7775" rel="noreferrer noopener nofollow">[email protected]</a>
     4           name         jack
     4           phone        123-4567
     4           email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="7e141f1d153e19131f1712501d1113" rel="noreferrer noopener nofollow">[email protected]</a>  

或者更好，如果我可以像这样组合行:

3           name         abe    3       email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="1c7d7e795c7b717d7570327f7371" rel="noreferrer noopener nofollow">[email protected]</a>
4           name         jack   4       phone        123-4567         4           email        <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="6c060d0f072c0b010d0500420f0301" rel="noreferrer noopener nofollow">[email protected]</a> 

Answer 1

这里的一个选项是使用子查询来识别最新的和紧邻最新的 submissionId:

SELECT submissionId, input, value
FROM yourTable
WHERE submissionId >= (SELECT MAX(submissionId) FROM yourTable) - 1
ORDER BY submissionId

此处演示:

SQLFiddle

更新:

如果您的 submissionId 列确实是日期类型，并且您想要结果集中最近的两个日期，那么以下查询将实现这一点。请注意，WHERE 子句中的子查询虽然丑陋，但与外部查询并不相关。这意味着 MySQL 优化器应该能够确定它只需要运行一次。

SELECT submissionDate, input, value
FROM yourTable
WHERE submissionDate >=
    (SELECT MAX(CASE WHEN submissionDate = (SELECT MAX(submissionDate) FROM yourTable)
                    THEN '1000-01-01'
                    ELSE submissionDate
               END) FROM yourTable)
ORDER BY submissionDate

SQLFiddle