Home Database Mysql Tutorial QL查询案例:取得分组 TOP-N

QL查询案例:取得分组 TOP-N

Jun 07, 2016 pm 05:37 PM
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【转】SQL查询案例:取得分组 TOP-N CREATE TABLE TopnTest ( name VARCHAR(10), --姓名 procDate DATETIME, --处理时间 result INT --成绩 ); INSERT INTO TopnTest VALUES('张三', '2010-10-01 12:00:05', 80); INSERT INTO TopnTest VALUES('张三', '2010

【转】SQL查询案例:取得分组 TOP-N

 

CREATE TABLE TopnTest (

name     VARCHAR(10),   --姓名

procDate DATETIME,       --处理时间

result   INT              --成绩

);

 

INSERT INTO TopnTest VALUES('张三', '2010-10-01 12:00:05', 80);

INSERT INTO TopnTest VALUES('张三', '2010-10-01 12:20:05', 85);

INSERT INTO TopnTest VALUES('张三', '2010-10-02 07:25:15', 79);

INSERT INTO TopnTest VALUES('张三', '2010-10-02 10:30:05', 88);

INSERT INTO TopnTest VALUES('张三', '2010-10-03 15:05:05', 86);

 

INSERT INTO TopnTest VALUES('李四', '2010-10-01 06:00:05', 60);

INSERT INTO TopnTest VALUES('李四', '2010-10-04 08:00:05', 90);

INSERT INTO TopnTest VALUES('李四', '2010-10-05 10:00:05', 75);

INSERT INTO TopnTest VALUES('李四', '2010-10-08 11:00:05', 88);

INSERT INTO TopnTest VALUES('李四', '2010-10-09 12:00:05', 60);

 

INSERT INTO TopnTest VALUES('王五', '2010-09-10 08:00:05', 70);

INSERT INTO TopnTest VALUES('王五', '2010-09-14 08:00:05', 80);

INSERT INTO TopnTest VALUES('王五', '2010-09-25 18:00:05', 75);

INSERT INTO TopnTest VALUES('王五', '2010-09-28 18:00:05', 88);

INSERT INTO TopnTest VALUES('王五', '2010-10-09 12:00:05', 70);

 

要求

取得每个人的最近2次处理时间的详细记录情况。

 

思路

如果仅仅是一个人的最近2次,那么直接TOP 2或者Rownum

每个人的最近1次,也可以通过SELECT MAX() GROUP BY来实现。

每个人的最近2次,需要自己和自己关联,才能解决了。

 

实现

SELECT

*

FROM

TopnTest

WHERE

( SELECT

      COUNT(1)

    FROM

      TopnTest subTopnTest

    WHERE

      TopnTest.name = subTopnTest.name

      AND TopnTest.procDate

)

ORDER BY

name, procDate

 

执行结果

name       procDate                result

---------- ----------------------- -----------

李四         2010-10-08 11:00:05.000          88

李四         2010-10-09 12:00:05.000          60

王五         2010-09-28 18:00:05.000          88

王五         2010-10-09 12:00:05.000          70

张三         2010-10-02 10:30:05.000          88

张三         2010-10-03 15:05:05.000          86

 

 

 

如果上面的 SQL , 你不怎么看得懂, 那么下面这样的写法,与执行结果,应该能让你更加容易明白一些上面的SQL的处理的原理。

 

SELECT 
  name,
  procDate,
  result,
  ( SELECT
      COUNT(1)
    FROM
      TopnTest subTopnTest
    WHERE
      TopnTest.name = subTopnTest.name
      AND TopnTest.procDate   ) AS [有多少行数据处理时间比当前行大]
FROM
  TopnTest
ORDER BY
  name, procDate

 

name       procDate                result      有多少行数据处理时间比当前行大
---------- ----------------------- ----------- ---------------
李四         2010-10-01 06:00:05.000          60               4
李四         2010-10-04 08:00:05.000          90               3
李四         2010-10-05 10:00:05.000          75               2
李四         2010-10-08 11:00:05.000          88               1
李四         2010-10-09 12:00:05.000          60               0
王五         2010-09-10 08:00:05.000          70               4
王五         2010-09-14 08:00:05.000          80               3
王五         2010-09-25 18:00:05.000          75               2
王五         2010-09-28 18:00:05.000          88               1
王五         2010-10-09 12:00:05.000          70               0
张三         2010-10-01 12:00:05.000          80               4
张三         2010-10-01 12:20:05.000          85               3
张三         2010-10-02 07:25:15.000          79               2
张三         2010-10-02 10:30:05.000          88               1
张三         2010-10-03 15:05:05.000          86               0

(15 行受影响)

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