MySQL-合并两个查询或限制结果

Question

I have a table that tracks recently updated pages, each page has a type. I want to limit the results so that we only pull 3 pages of type x, and 3 of type y, but still have them sorted by lastUpdated. I can't figure out how to do this in mysql

SELECT * from recentlyUpdated WHERE type = 'x' DESC LIMIT 3
SELECT * from recentlyUpdated WHERE type = 'y' DESC LIMIT 3

then ...

ORDER BY lastUpdated DESC

Answer 1

This may help you;)

(SELECT * from recentlyUpdated WHERE type = 'x'lastUpdated ORDER BY DESC LIMIT 3)
UNION ALL
(SELECT * from recentlyUpdated WHERE type = 'y'lastUpdated ORDER BY DESC LIMIT 3)
ORDER BY lastUpdated DESC

Answer 2

One obvious way to do it is using UNION :

SELECT *
FROM (
  SELECT * 
  FROM recentlyUpdated 
  WHERE type = 'x'  
  LIMIT 3

  UNION ALL

  SELECT * 
  FROM recentlyUpdated 
  WHERE type = 'y' 
  LIMIT 3) AS t
ORDER BY lastUpdated DESC

Alternatively, you can use variables:

  SELECT *
  FROM (
    SELECT *,
           @seq := IF(@t = type, @seq + 1,
                      IF(@t := type, 1, 1)) AS seq 
    FROM recentlyUpdated 
    CROSS JOIN (SELECT @seq := 0, @t := '') AS vars
    WHERE type IN ('x', 'y')
    ORDER BY type) AS t
  WHERE t.seq <= 3
  ORDER BY lastUpdated DESC