Question

如果JOIN categories c ON c.id = i.category为1，我希望使用post_type我希望c.title AS category_name,中SELECT JOIN categories c ON c.id = i.category，c.title AS category_name,和post_type必须没有在查询中工作，我使用case加入但我的sql命令不正确。请帮我。在所有描述中，我的quastion意味着如何更改以下命令，如果SELECT SQL_CALC_FOUND_ROWS i. * , c.title AS category_name, s.title AS status_title, i.thumb_image, CONCAT( u.name, ' ', u.family ) AS author FROM contents i LEFT JOIN categories c ON i.category = CASE post_type WHEN 1 then c.id END JOIN users u ON u.id = i.posted_by JOIN status_topics s ON s.id = i.t_status WHERE i.id = 2是1加入必须不起作用

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Answer 1

我会一直做LEFT JOIN并在列本身上加上一个条件：

SELECT SQL_CALC_FOUND_ROWS
   i. * , 
   IF(i.post_type = 1, c.title, NULL) AS category_name, 
   s.title AS status_title, 
   i.thumb_image, 
   CONCAT( u.name, ' ', u.family ) AS author
FROM contents i
LEFT JOIN categories c ON i.category = c.id
JOIN users u ON u.id = i.posted_by
JOIN status_topics s ON s.id = i.t_status
WHERE i.id = 2

MYSQL可自定义加入和选择

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