Question

请原谅我对此缺乏了解。我对PHP和MySQL查询的经验有限。我可以做一些基本的查询，但是，这是我需要修改的，这让我感到困惑。

我有一个查询，它会为已分配奖励的产品提取所有数据。但是，如果一个产品有多个奖项，则会多次显示该产品。理想情况下，我希望该产品能够展示一次。

我希望将DISTINCT或UNIQUE值应用于查询，但是构造查询的方式，它似乎没有做任何事情。

原始查询如下：

<?php
                    $get_awards = $wpdb->get_results("
SELECT * 
  FROM wp_posts 
 WHERE post_type = 'award' 
   AND post_status = 'publish' 
   AND YEAR(CAST(post_date AS DATE))=2009 
 GROUP 
    BY post_title 
 ORDER 
    BY post_date DESC
");
                    foreach ($get_awards as $award) {
                        $get_products = $wpdb->get_results("SELECT * FROM wp_posts INNER JOIN wp_postmeta ON wp_posts.ID = wp_postmeta.post_id WHERE post_type = 'ice-cream' AND post_status = 'publish' AND meta_key = 'awards' AND meta_value LIKE '%''".$award->ID."''%' OR post_type = 'frozen-yoghurt' AND post_status = 'publish' AND meta_key = 'awards' AND meta_value LIKE '%''".$award->ID."''%' OR post_type = 'sorbet' AND post_status = 'publish' AND meta_key = 'awards' AND meta_value LIKE '%''".$award->ID."''%'");
                        foreach ($get_products as $product) { ?>

我尝试了几个版本的SELECT * for SELECT DISTINCT等，但没有快乐。请问中间有人指点我吗？

Answer 1

如果你*选择了所有列，那么distinct是无用的

如果您需要不同的结果，则应明确选择您想要不同值的列

Group by is for aggreagtion function and is not necessary  for distinct clause

所以，你需要的列是col1，col2和col3，你应该使用像

这样的选择

    SELECT DISTINCT col1, col2, col2 
    FROM wp_posts 
    WHERE post_type = 'award' 
    AND post_status = 'publish' 
    AND YEAR(CAST(post_date AS DATE))=2009 
    GROUP BY post_title 
    ORDER BY post_date DESC

MySQL独特的内部联接

1 个答案: