MySQL查詢爲獲得一類

Question

的頂部實例我有一個表像下面：

COL1 | COL2 | COL3 
______________________ 
ITEM1 | CLASS1 | DATE1 
ITEM2 | CLASS3 | DATE2 
ITEM3 | CLASS1 | DATE3 
ITEM4 | CLASS2 | DATE4 
ITEM5 | CLASS1 | DATE2 
ITEM6 | CLASS3 | DATE6 
ITEM7 | CLASS2 | DATE3 
. 
. 

我想安排由降日的數據，然後獲得前2項，每類。我無法弄清楚如何做到這一點。請幫忙。

Answer 1

試試這個查詢，它將它記錄在一個組中，然後用排名來過濾結果 -

SELECT col1, col2, col3 FROM (
    SELECT e1.*, COUNT(*) p FROM entries e1 
    LEFT JOIN entries e2 
     ON e1.col2 = e2.col2 AND e1.col3 <= e2.col3 
    GROUP BY e1.col2, e1.col3 
) t 
WHERE p < 3 

+-------+--------+-------+ 
| col1 | col2 | col3 | 
+-------+--------+-------+ 
| ITEM5 | CLASS1 | DATE2 | 
| ITEM3 | CLASS1 | DATE3 | 
| ITEM7 | CLASS2 | DATE3 | 
| ITEM4 | CLASS2 | DATE4 | 
| ITEM2 | CLASS3 | DATE2 | 
| ITEM6 | CLASS3 | DATE6 | 
+-------+--------+-------+ 

Answer 2

Didnt嘗試，請給一個嘗試：

SELECT t.*, max(col3) as `date` /* Most recent date */ 
    FROM table t 
    GROUP BY col2 

UNION 

SELECT t2.*, max(col3) as `date` /* second recent date */ 
    FROM table t2 
    WHERE col3 NOT IN 
    (SELECT max(col3) WHERE col2 = t2.col2 GROUP BY col2) 
    GROUP BY col2 

Answer 3

嘗試......

(
SELECT t1.* FROM the_table t1 
    LEFT JOIN the_table t2 ON t2.col2=t1.col2 AND t2.col3<t1.col3 
    LEFT JOIN the_Table t3 ON t3.col2=t2.col2 AND t3.col3<t2.col3 
WHERE t3.col2 IS NULL AND t2.col2 IS NOT NULL 
ORDER BY t1.col2,t1.col3 DESC 
) 
UNION 
(
SELECT t4.* FROM the_table t4 
    LEFT JOIN the_table t5 ON t4.col2=t5.col2 AND t4.col1!=t5.col1 
    LEFT JOIN the_Table t6 ON t5.col2=t6.col2 AND t5.col1!=t6.col1 
WHERE t6.col1 IS NULL 
ORDER BY t4.col3 DESC 
) 

注：在聯盟第二部分是用於提取具有小於3點的記錄每行class