mysql - SQL查询: how to group items correctly?

Question

您能否帮忙修改以下 SQL 查询，使其能够在 mySQL 中运行？目前，错误信息是表t1不存在。我想要一个包含“post_title”、“name1”、“url1”列的表格。

如果有帮助，则可以在 Wordpress CMS 数据库上测试此查询

SELECT t1.post_title,
       (select meta_value from t1 where t1.meta_key='name1_class' limit 1) as name1,
       (select meta_value from t1 where t1.meta_key='url1_class' limit 1) as url1
  FROM (select pm.post_id as id, pm.meta_key, pm.meta_value, p.post_title, t.slug from wp_2_postmeta pm
    inner join wp_2_posts p on pm.post_id = p.id
    inner join wp_2_term_relationships tr on tr.object_id = p.id    
    inner join wp_2_term_taxonomy tt on tr.term_taxonomy_id = tt.term_taxonomy_id
    inner join wp_2_terms t on t.term_id = tt.term_id
    where post_type='footercolumn' and post_status='publish' and pm.meta_key like '%class') t1 

“FROM”子句中 t1 表的子查询生成如下数据集:

'id', 'meta_key',  'meta_value', 'post_title', 'slug' 
'18', 'name1_class', 'Our Work', 'Who we are', 'column1' 
'18', 'url1_class', '/work.html', 'Who we are', 'column1' 
'18', 'name1_class', 'Our Team', 'About', 'column2' 
'18', 'url1_class', 'team.html', 'About', 'column2

我希望结果表是:

'title',      'name1',     'url1'
'Who we are', 'Our Work',  'work.html'
'About',      'Our Team',  'team.html'

谢谢

Answer 1

看起来您正在尝试使用子选择来模拟 CTE(公共(public)表表达式)，但我不太想出一种方法来实现这一点。

好消息是，如果您可以使用聚合来查找数据，则不需要子选择。

SELECT t1.post_title,
       MAX(CASE WHEN meta_key='name1_class' THEN meta_value END) as name1,
       MAX(CASE WHEN meta_key='url1_class' THEN meta_value END) as url1
  FROM (select pm.post_id as id, pm.meta_key, pm.meta_value, p.post_title, t.slug 
        from wp_2_postmeta pm
        inner join wp_2_posts p on pm.post_id = p.id
        inner join wp_2_term_relationships tr on tr.object_id = p.id    
        inner join wp_2_term_taxonomy tt 
           on tr.term_taxonomy_id = tt.term_taxonomy_id
        inner join wp_2_terms t on t.term_id = tt.term_id
        where post_type='footercolumn' and post_status='publish' and pm.meta_key 
              like '%class') t1