さて、私は問題で遊んで、いくつかの提案があります。しかし、最初にヘルパーテーブルを作成しましょう
CREATE TABLE dbo.Numbers(n INT NOT NULL PRIMARY KEY)
GO
DECLARE @i INT;
SET @i = 1;
INSERT INTO dbo.Numbers(n) SELECT 1;
WHILE @i<1024000 BEGIN
INSERT INTO dbo.Numbers(n)
SELECT n + @i FROM dbo.Numbers;
SET @i = @i * 2;
END;
GO
およびテスト データ、1 年間の毎分 1 分間のコマーシャル、および同じ年の 1 分間に 1 回の顧客コール:
CREATE TABLE dbo.Commercials(
StartedAt DATETIME NOT NULL
CONSTRAINT PK_Commercials PRIMARY KEY,
EndedAt DATETIME NOT NULL,
CommercialName VARCHAR(30) NOT NULL);
GO
INSERT INTO dbo.Commercials(StartedAt, EndedAt, CommercialName)
SELECT DATEADD(minute, n - 1, '20080101')
,DATEADD(minute, n, '20080101')
,'Show #'+CAST(n AS VARCHAR(6))
FROM dbo.Numbers
WHERE n<=24*365*60;
GO
CREATE TABLE dbo.Calls(CallID INT
CONSTRAINT PK_Calls NOT NULL PRIMARY KEY,
AirTime DATETIME NOT NULL,
SomeInfo CHAR(300));
GO
INSERT INTO dbo.Calls(CallID,
AirTime,
SomeInfo)
SELECT n
,DATEADD(minute, n - 1, '20080101')
,'Call during Commercial #'+CAST(n AS VARCHAR(6))
FROM dbo.Numbers
WHERE n<=24*365*60;
GO
CREATE UNIQUE INDEX Calls_AirTime
ON dbo.Calls(AirTime) INCLUDE(SomeInfo);
GO
年の半ばの 3 時間のコマーシャル中にかけられたすべての通話を選択する最初の試みは、非常に遅いです。
SET STATISTICS IO ON;
SET STATISTICS TIME ON;
GO
SELECT COUNT(*) FROM(
SELECT s.StartedAt, s.EndedAt, c.AirTime
FROM dbo.Commercials s JOIN dbo.Calls c
ON c.AirTime >= s.StartedAt AND c.AirTime < s.EndedAt
WHERE c.AirTime BETWEEN '20080701' AND '20080701 03:00'
) AS t;
SQL Server parse and compile time:
CPU time = 15 ms, elapsed time = 30 ms.
(1 row(s) affected)
Table 'Calls'. Scan count 1, logical reads 11, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 2, logical reads 3338264, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Commercials'. Scan count 2, logical reads 7166, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
SQL Server Execution Times:
CPU time = 71704 ms, elapsed time = 36316 ms.
理由は簡単です。コマーシャルが重複しないことがわかっているため、1 つの呼び出しが多くても 1 つのコマーシャルに収まりますが、オプティマイザーはそれを知りません。コマーシャルが短いことはわかっていますが、オプティマイザーもそれを知りません。どちらの仮定も制約として適用できますが、オプティマイザーはそれを実行しません。
コマーシャルが 15 分以内であると仮定すると、オプティマイザーにそれを伝えることができ、クエリは非常に高速です。
SELECT COUNT(*) FROM(
SELECT s.StartedAt, s.EndedAt, c.AirTime
FROM dbo.Commercials s JOIN dbo.Calls c
ON c.AirTime >= s.StartedAt AND c.AirTime < s.EndedAt
WHERE c.AirTime BETWEEN '20080701' AND '20080701 03:00'
AND s.StartedAt BETWEEN '20080630 23:45' AND '20080701 03:00'
) AS t;
SQL Server parse and compile time:
CPU time = 15 ms, elapsed time = 15 ms.
(1 row(s) affected)
Table 'Worktable'. Scan count 1, logical reads 753, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Calls'. Scan count 1, logical reads 11, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Commercials'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
SQL Server Execution Times:
CPU time = 31 ms, elapsed time = 24 ms.
コマーシャルが重複しないため、1 つの呼び出しが多くても 1 つのコマーシャルに収まると仮定すると、オプティマイザーにそれを伝えることができ、クエリは再び非常に高速になります。
SELECT COUNT(*) FROM(
SELECT s.StartedAt, s.EndedAt, c.AirTime
FROM dbo.Calls c CROSS APPLY(
SELECT TOP 1 s.StartedAt, s.EndedAt FROM dbo.Commercials s
WHERE c.AirTime >= s.StartedAt AND c.AirTime < s.EndedAt
ORDER BY s.StartedAt DESC) AS s
WHERE c.AirTime BETWEEN '20080701' AND '20080701 03:00'
) AS t;
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 7 ms.
(1 row(s) affected)
Table 'Commercials'. Scan count 181, logical reads 1327, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Calls'. Scan count 1, logical reads 11, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
SQL Server Execution Times:
CPU time = 31 ms, elapsed time = 31 ms.