Question

我通过3个查询访问我网站上的数据，首先查询获得网站上可用的完整交易列表：

  $listingquery = "SELECT * FROM table WHERE city = '$city' AND approved = '1' 
  AND enddate > NOW() ORDER BY id DESC";

下一个查询获取可用交易提供者的计数/列表：

  $providerquery = "SELECT  programname, category, COUNT(name) FROM table WHERE 
  city = '$city' AND approved='1' AND enddate > NOW() GROUP BY provider";

和第三个查询从该城市的可用交易提供商处获取类别的计数/列表：

  $categoryquery = "SELECT  programname, category, COUNT(name) FROM table WHERE 
  city = '$city' AND approved='1' AND enddate > NOW() GROUP BY category";

有没有办法将所有这些组合成1个查询？

提前致谢！

Answer 1

您可能会获得一些无损信息，但您可以尝试这样做：

 SELECT * FROM table a
  LEFT JOIN (
    SELECT  programname, category, COUNT(name) 
     FROM table 
     WHERE city = '$city' AND approved='1' AND enddate > NOW() GROUP BY provider
  ) b ON a.provider = b.provider
  LEFT JOIN (
    SELECT  programname, category, COUNT(name) 
     FROM table 
     WHERE city = '$city' AND approved='1' AND enddate > NOW() GROUP BY category
  ) c ON a.category = b.category
  WHERE a.city = '$city' AND a.approved = '1' 
    AND a.enddate > NOW() 
  ORDER BY a.id DESC;

使用一个Where子句更新（有点）：

 SELECT * FROM table a
  LEFT JOIN (
    SELECT  programname, category, COUNT(name) 
     FROM table 
     WHERE enddate > NOW() GROUP BY provider
  ) b ON a.provider = b.provider
  LEFT JOIN (
    SELECT  programname, category, COUNT(name) 
     FROM table 
     WHERE enddate > NOW() GROUP BY category
  ) c ON a.category = b.category
  WHERE a.city = '$city' AND a.approved = '1' 
    AND a.enddate > NOW() 
    AND b.city = a.city AND c.city = a.city
    AND b.approved = a.approved AND c.approved = a.approved
  ORDER BY a.id DESC;

Answer 2

我怀疑所有这些在单个查询中是可行/可行的，但无论哪种方式，您都不应该在MySQL中使用子查询，这将极大地降低性能。首选加入而不是子查询。

加入mysql子查询

2 个答案: