我无法让 @Alex W 的查询正常工作。它不是标准的 SQL 语句，因此需要大量修改以兼容 SQL Server（我可以测试）。但它确实启发了我，我进行了扩展。
查找每个连续等待期的起始点：
SELECT DISTINCT
t1.ID,
t1.d1 AS date,
-DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d1) AS n
FROM Orders t1
LEFT JOIN Orders t2
ON t2.ID = t1.ID
AND t2.d1 <> t1.d1
AND t1.d1 BETWEEN t2.d1 AND t2.d2
GROUP BY t1.ID, t1.d1, t1.d2
HAVING COUNT(t2.ID) = 0
以及端点的对应项：
SELECT DISTINCT
t1.ID,
t1.d2 AS date,
DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d2) AS n
FROM Orders t1
LEFT JOIN Orders t2
ON t2.ID = t1.ID
AND t2.d2 <> t1.d2
AND t1.d2 BETWEEN t2.d1 AND t2.d2
GROUP BY t1.ID, t1.d1, t1.d2
HAVING COUNT(t2.ID) = 0
n 是距离某个共同时间点的天数。起始点具有负值，而结束点具有正值。这是为了方便我们将它们相加以得到它们之间的天数。
span = end - start
span = end + (-start)
span1 + span2 = end1 + (-start1) + end2 + (-start2)
最后，我们只需要把所有的东西加起来：
SELECT ID, SUM(n) AS hold_days
FROM (
SELECT DISTINCT
t1.id,
t1.d1 AS date,
-DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d1) AS n
FROM Orders t1
LEFT JOIN Orders t2
ON t2.ID = t1.ID
AND t2.d1 <> t1.d1
AND t1.d1 BETWEEN t2.d1 AND t2.d2
GROUP BY t1.ID, t1.d1, t1.d2
HAVING COUNT(t2.ID) = 0
UNION ALL
SELECT DISTINCT
t1.id,
t1.d2 AS date,
DATEDIFF(DAY, (SELECT MIN(d1) FROM Orders), t1.d2) AS n
FROM Orders t1
LEFT JOIN Orders t2
ON t2.ID = t1.ID
AND t2.d2 <> t1.d2
AND t1.d2 BETWEEN t2.d1 AND t2.d2
GROUP BY t1.ID, t1.d1, t1.d2
HAVING COUNT(t2.ID) = 0
ORDER BY ID, date
) s
GROUP BY ID;
输入表（订单）：
ID d1 d2
1 2011-08-01 2011-08-08
1 2011-08-02 2011-08-06
1 2011-08-03 2011-08-10
1 2011-08-12 2011-08-14
2 2011-08-01 2011-08-03
2 2011-08-02 2011-08-06
2 2011-08-05 2011-08-09
输出：
ID hold_days
1 11
2 8
或者，您可以使用存储过程完成此操作。
CREATE PROCEDURE CalculateHoldTimes
@ID int = 0
AS
BEGIN
DECLARE Events CURSOR FOR
SELECT *
FROM (
SELECT d1 AS date, 1 AS diff
FROM Orders
WHERE ID = @ID
UNION ALL
SELECT d2 AS date, -1 AS diff
FROM Orders
WHERE ID = @ID
) s
ORDER BY date;
DECLARE @Events_date date,
@Events_diff int,
@Period_start date,
@Period_accum int,
@Total_start date,
@Total_count int;
OPEN Events;
FETCH NEXT FROM Events
INTO @Events_date, @Events_diff;
SET @Period_start = @Events_date;
SET @Period_accum = 0;
SET @Total_start = @Events_date;
SET @Total_count = 0;
WHILE @@FETCH_STATUS = 0
BEGIN
SET @Period_accum = @Period_accum + @Events_diff;
IF @Period_accum = 1 AND @Events_diff = 1
SET @Period_start = @Events_date;
ELSE IF @Period_accum = 0 AND @Events_diff = -1
SET @Total_count = @Total_count +
DATEDIFF(day, @Period_start, @Events_date);
FETCH NEXT FROM Events
INTO @Events_date, @Events_diff;
END;
SELECT
@Total_start AS d1,
@Events_date AS d2,
@Total_count AS hold_time;
END;
使用以下命令调用：
EXEC CalculateHoldTimes 1;
