Question

首先，我对SQL不是很熟悉。我之前在这里找到了类似的问题，但到目前为止，我无法为我的具体问题开发出一个可行的解决方案。

我有一个表格，其中包含电话记录，其中包含以下字段：

 END: Holds the timestamp of when a call ended - Data Type: DATE
 LINE: Holds the phone line that was used for a call - Data Type: NUMBER
 CALLDURATION: Holds the duration of a call in seconds - Data Type: NUMBER

该表包含以下条目：

END                    LINE                CALLDURATION
---------------------- ------------------- -----------------------
25/01/2012 14:05:10    6                   65
25/01/2012 14:08:51    7                   1142
25/01/2012 14:20:36    5                   860

我需要创建一个查询，根据该表中的数据返回并发电话的数量。查询应该能够以固定间隔计算该数字，例如每5分钟计算一次。为了更清楚，这里是一个查询应返回的示例（基于上表中的示例条目：

TIMESTAMP              CURRENTLYUSEDLINES          
---------------------- -------------------
25/01/2012 14:05:00    2
25/01/2012 14:10:00    1
25/01/2012 14:15:00    1

如何使用（Oracle）SQL查询执行此操作？表中目前有近100万条记录，因此查询必须尽可能快，否则执行它会花费很长时间。

Answer 1

一个解决方案就是这个：

WITH t AS
    (SELECT TIMESTAMP '2012-01-25 14:00:00' + LEVEL * INTERVAL '5' MINUTE AS TS
    FROM dual
    CONNECT BY TIMESTAMP '2012-01-25 14:00:00' + LEVEL * INTERVAL '5' MINUTE <= TIMESTAMP '2012-01-25 14:15:00'),
calls AS 
    (SELECT TIMESTAMP '2012-01-25 14:05:10' AS END_TIME, 6 AS LINE, 65 AS duration FROM dual
    UNION ALL SELECT TIMESTAMP '2012-01-25 14:08:51', 7, 1142 FROM dual
    UNION ALL SELECT TIMESTAMP '2012-01-25 14:20:36', 5, 860 FROM dual)
SELECT TS, count(distinct line)
FROM t
    LEFT OUTER JOIN calls ON ts BETWEEN END_TIME - duration * INTERVAL '1' SECOND AND END_TIME
GROUP BY ts
HAVING count(distinct line) > 0
ORDER BY ts;

TS                   COUNT(DISTINCTLINE)
-------------------- -------------------
25.01.2012 14:05:00                    2
25.01.2012 14:10:00                    1
25.01.2012 14:15:00                    1

3 rows selected.

Oracle SQL - 计算并发电话呼叫数

1 个答案: