Question

这是我目前的查询：

SELECT 
  topic.title, 
  topic.content_id, 
  topic.thumbnail_icon, 
  text.description 
FROM 
  mps_contents AS topic, 
  mps_contents AS text 
WHERE 
  topic.featured = '1' AND 
  topic.active = '1' AND 
  topic.page_id = (SELECT page_id 
                     FROM mps_pages 
                    WHERE page_short_name = 'services' 
                       OR page_short_name = 'questions_faqs') AND 
  text.section_id = (SELECT section_id 
                       FROM mps_sections 
                      WHERE section_short_name = 'page_text') AND 
  text.page_id = topic.content_id AND 
  topic.resource_type = 'subpage' AND 
  text.resource_type = 'text' 
ORDER BY RAND() LIMIT 2

修改
这是MySQL

我真正想做的是从services中选择1个特色项目和从questions中选择1个特色项目。不过，此查询会从services或questions中选择2个特色商品！

我知道一个选项是在UNION的两个查询中生成LIMIT 1并执行UNION，但这意味着我必须复制90％的查询。我可以这样做，而不必诉诸UNION s？

Answer 1

好吧，我相信除非你重新设计/规范化表格，否则你总会在某种程度上重复查询。

如果你想避免结合，你可以重写

  topic.page_id = (SELECT page_id 
                 FROM mps_pages 
                WHERE page_short_name = 'services' 
                   OR page_short_name = 'questions_faqs')

到

topic.page_id = (SELECT page_id 
                 FROM mps_pages 
                 WHERE page_short_name = 'services' ORDER BY RAND() LIMIT 1)
                   OR 
topic.page_id = (SELECT page_id 
                 FROM mps_pages 
                 WHERE page_short_name = 'questions_faqs' ORDER BY RAND() LIMIT 1)

虽然rand（）运行两次

，但我认为不会有太多的性能提升

从WHERE子句的每个条件中精确选择一个项目

1 个答案: