Question

我在MySql（events和special_events）中有2个表没有相同数量的列（special_events有一个唯一的datetime列 - 排除UNION），但是我想将两个表合并在一起并返回组合结果生成以下共享列：title，parent和directory ...

SELECT title, parent, root 
FROM events 
WHERE root != "services" 
ORDER BY RAND() LIMIT 10

我需要在这里使用什么类型的JOIN。

NB。 special_events还有title，parent，root列等。

Answer 1

您可能需要这样的查询：

SELECT *
FROM (
  SELECT title, parent, root 
  FROM events
  WHERE root != 'services'
  UNION ALL
  SELECT title, parent, root 
  FROM special_events
  WHERE root != 'services'
) s
ORDER BY RAND()
LIMIT 10

Answer 2

您还可以从special_events中获取唯一的日期时间列，例如

SELECT *
FROM (
  SELECT title, parent, root, NULL as datetime_column
  FROM events
  WHERE root != 'services'
  UNION ALL
  SELECT title, parent, root, datetime_column
  FROM special_events
  WHERE root != 'services'
) s
ORDER BY RAND()
LIMIT 10

在MySql中加入 - 哪一个？

2 个答案: