SQL-选择x个具有公共列值的最新行

Question

Example

I would like to select the 5 most recent rows that have the same group value from the following table.

--------------------------------------------
|    id    |    group    |    timestamp    |
--------------------------------------------
|    1     |    circle   |    1468287300   |
|    2     |    square   |    1468287816   |
|    3     |    square   |    1468287694   |
|    4     |    circle   |    1468287252   |
|    5     |    circle   |    1468287987   |
|    6     |    circle   |    1468287068   |
|    7     |    square   |    1468287149   |
|    8     |    circle   |    1468287422   |
--------------------------------------------

Answer 1

我认为这应该可行，请检查并告知我

SELECT * FROM Table1 GROUP BY group ORDER BY timestamp DESC LIMIT 5;

Answer 2

Try this:

SELECT t.`id`, t.`group`, t.`timestamp`
FROM (
   SELECT
        t1.*,
        IF(@grp = `group`, @rowno := @rowno + 1, @rowno := 1) AS rowno,
        @grp := `group`
    FROM (
        SELECT *
        FROM yourtable
        ORDER BY `group`, `timestamp` DESC
    ) t1
    CROSS JOIN (SELECT @grp := null, @rowno := 0) t2
) t
WHERE rowno < 6

SQLFiddle Demo