MySQL 连接和来自连接的子查询

Question

这是my earlier question的后续行动：

SELECT s.unique_id, s.counter, s.sequence_length, s.yearmonth, s.mod_date_stamp,
  pg1.page_url as page1, pg2.page_url as page2, pg3.page_url as page3,
  pg4.page_url as page4, pg5.page_url as page5
FROM session s
  LEFT JOIN sessionpage pg1 ON pg1.unique_id = s.page1 
  LEFT JOIN sessionpage pg2 ON pg2.unique_id = s.page2
  LEFT JOIN sessionpage pg3 ON pg3.unique_id = s.page3
  LEFT JOIN sessionpage pg4 ON pg4.unique_id = s.page4
  LEFT JOIN sessionpage pg5 ON pg5.unique_id = s.page5

可以很好地显示整个表格。现在，我需要select s.unique_id WHERE page1=/path/to/something.html AND page2=/path/to/somethingelse.html。

我不知道如何只返回unique_id 而不返回整个表。我知道我需要一个嵌套查询，但我不知道语法。

它应该看起来像：

SELECT s.unique_id 
  (SELECT pg1.page_url as page1, pg2.page_url as page2, pg3.page_url as page3,
    pg4.page_url as page4, pg5.page_url as page5 FROM session201203) s
  LEFT JOIN sessionpage pg1 ON pg1.unique_id = s.page1 
  LEFT JOIN sessionpage pg2 ON pg2.unique_id = s.page2 
  LEFT JOIN sessionpage pg3 ON pg3.unique_id = s.page3 
  LEFT JOIN sessionpage pg4 ON pg4.unique_id = s.page4 
  LEFT JOIN sessionpage pg5 ON pg5.unique_id = s.page5
WHERE s.sequence_length = 2 AND s.page1 = '/path1.html' AND s.page2 = '/path2.html';

但是这个查询失败了，因为它在加入之前试图找到 pg1 等。我已经尝试了很多东西，但无法弄清楚。再次感谢。

Answer 1

试试这个：在最后一个连接之后移动括号) s

SELECT s.unique_id 
  FROM (SELECT pg1.page_url as page1, pg2.page_url as page2, pg3.page_url as page3,
    pg4.page_url as page4, pg5.page_url as page5 FROM session201203
  LEFT JOIN sessionpage pg1 ON pg1.unique_id = s.page1 
  LEFT JOIN sessionpage pg2 ON pg2.unique_id = s.page2 
  LEFT JOIN sessionpage pg3 ON pg3.unique_id = s.page3 
  LEFT JOIN sessionpage pg4 ON pg4.unique_id = s.page4 
  LEFT JOIN sessionpage pg5 ON pg5.unique_id = s.page5) s
WHERE s.sequence_length = 2 AND s.page1 = '/path1.html' AND s.page2 = '/path2.html';