3

我有这个样本数据

+------+------------+------------+
| CODE | START_DATE | END_DATE   |
+------+------------+------------+
| 0001 | 2012-01-01 | 2012-01-31 |
+------+------------+------------+
| 0001 | 2012-02-01 | 2012-02-29 |
+------+------------+------------+
| 0001 | 2012-03-01 | NULL       |
+------+------------+------------+
| 0002 | 2012-02-01 | 2012-02-29 |
+------+------------+------------+
| 0002 | 2012-03-01 | 2012-03-31 |
+------+------------+------------+
| 0002 | 2012-04-01 | NULL       |
+------+------------+------------+
| 0003 | 2012-02-01 | 2012-02-29 |
+------+------------+------------+
| 0003 | 2012-03-01 | 2012-03-31 |
+------+------------+------------+

DDL

CREATE TABLE SAMPLE
(
    CODE VARCHAR(4),
    START_DATE DATETIME,
    END_DATE DATETIME
)

INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0001', {d '2012-01-01'}, {d '2012-01-31'})
INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0001', {d '2012-02-01'}, {d '2012-02-29'})
INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0001', {d '2012-03-01'}, NULL)

INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0002', {d '2012-02-01'}, {d '2012-02-29'})
INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0002', {d '2012-03-01'}, {d '2012-03-31'})
INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0002', {d '2012-04-01'}, NULL)

INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0003', {d '2012-02-01'}, {d '2012-02-29'})
INSERT INTO SAMPLE (CODE, START_DATE, END_DATE) VALUES ('0003', {d '2012-03-01'}, {d '2012-03-31'})

我希望得到这些数据

+------+------------+------------+
| CODE | START_DATE | END_DATE   |
+------+------------+------------+
| 0001 | 2012-01-01 | NULL       |
+------+------------+------------+
| 0002 | 2012-02-01 | NULL       |
+------+------------+------------+
| 0003 | 2012-02-01 | 2012-03-31 |
+------+------------+------------+

目前在SQL Server 2005中，我使用这个查询

SELECT  CODE,
        MIN(START_DATE) AS START_DATE,
        CASE
            WHEN    MAX(ISNULL(END_DATE, {d '9999-12-31'})) = {d '9999-12-31'}
            THEN    NULL
        ELSE
            MAX(END_DATE)
        END AS END_DATE
FROM    SAMPLE
GROUP BY    CODE

迄今为止，我在欺骗NULL 值 9999-12-31

我正在为此寻找更好的解决方案

谢谢你

4

2 回答 2

1

COUNT您可以利用ofNULL和NOT NULL列不同的事实。所以脚本可以是这样的：

SELECT  CODE,
        MIN(START_DATE) AS START_DATE,
        CASE 
            WHEN    COUNT(*) > COUNT(END_DATE)
            THEN    NULL
        ELSE
            MAX(END_DATE)
        END AS END_DATE
FROM    SAMPLE
GROUP BY    CODE
于 2012-12-03T10:04:26.053 回答
0

此脚本使用 cte（公用表表达式）首先获取 null end_dates 并对其进行左连接。它消除了您使用的硬编码任意日期的需要。

由于它需要额外的查询，因此它会比您的初始解决方案慢。

因此，在决定最佳解决方案时，它还取决于记录的数量和调用此脚本的频率。

;WITH NULL_END_DATES_CTE AS (SELECT CODE FROM SAMPLE WHERE END_DATE IS NULL)
SELECT  S.CODE,
    MIN(S.START_DATE) AS START_DATE,
    CASE WHEN C.CODE IS NULL THEN MAX(S.END_DATE) ELSE NULL END AS END_DATE
FROM    SAMPLE S
LEFT JOIN NULL_END_DATES_CTE C ON C.CODE = S.CODE 
GROUP BY S.CODE,C.CODE
ORDER BY S.CODE
于 2012-11-30T06:09:17.977 回答