使用 MySQL 选择最后 5 个条目的总和的最大值？

Question

嘿，我不是 MySQL 的最大专家，但这是我迄今为止获得 MAX 输入的内容

   SELECT DISTINCT 
          websites.id, 
          websites.title, 
          websites.url, 
          websites.screenshot, 
          impressions.number, 
          blocks.price 
     FROM websites 
LEFT JOIN blocks ON websites.id = blocks.website 
LEFT JOIN impressions ON blocks.id = impressions.block 
    WHERE status = 1 
      AND blocks.active = '1' 
      AND impressions.number = (SELECT MAX(number) 
                                  FROM impressions)

我想要做的是 SELECT max(number) 但最后 5 个条目的总和。我尝试过乱搞，但就是无法得到它。

Answer 1

最后五个印象。数字这应该做它不知道你想要总结什么，但

SELECT DISTINCT websites.id, 
                websites.title, 
                websites.url, 
                websites.screenshot, 
                impressions.number, 
                blocks.price 
FROM   websites 
       LEFT JOIN blocks 
         ON websites.id = blocks.website 
       LEFT JOIN impressions 
         ON blocks.id = impressions.block 
WHERE  status = 1 
       AND blocks.active = '1' 
ORDER  BY impressions.number 
LIMIT  5 

如果你想总结块。价格你可以这样做

 SELECT SUM(lastblocks.price) 
   FROM (
    SELECT 
          price
    FROM   websites 
           LEFT JOIN blocks 
             ON websites.id = blocks.website 
           LEFT JOIN impressions 
             ON blocks.id = impressions.block 
    WHERE  status = 1 
           AND blocks.active = '1' 
    ORDER  BY impressions.number 
    LIMIT  5 ) lastblocks

Answer 2

要获取最后 5 条记录，这取决于您排序所依据的列。假设这是一个日期列，那么一个例子是：

SELECT MAX(n) FROM tbl ORDER BY datecol DESC limit 5;