ID が 2 番目のテーブルに存在する行を選択する最も効率的な方法

まとめ:

以下のテスト データ セットを使用して、各クエリをそれぞれ 10 回実行しました。

上記のすべてのシナリオで、両方の IN そしてEXISTS

Performance V3 データベース に関する情報 テストに使用されます。20000 人の顧客が 1000000 の注文を持っているため、各顧客は注文テーブルで (10 から 100 の範囲で) ランダムに複製されます。

実行コスト、時間:
以下は、実行中の両方のクエリのスクリーンショットです。各クエリの相対コストを観察します。

メモリ コスト:
2 つのクエリのメモリ許可も同じです..TEMPDB に流出しないように MDOP 1 を強制しました..

CPU 時間、読み取り:

存在する場合:

Table 'Workfile'. 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.
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.
Table 'Customers'. Scan count 1, logical reads 109, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Orders'. Scan count 1, logical reads 3855, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(1 row(s) affected)

 SQL Server Execution Times:
   CPU time = 469 ms,  elapsed time = 595 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

インの場合:

(20000 row(s) affected)
Table 'Workfile'. 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.
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.
Table 'Customers'. Scan count 1, logical reads 109, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Orders'. Scan count 1, logical reads 3855, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(1 row(s) affected)

 SQL Server Execution Times:
   CPU time = 547 ms,  elapsed time = 669 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

いずれの場合も、オプティマイザはクエリを再配置するほどスマートです。

EXISTS をよく使用します ただし（私の意見）。 EXISTS を使用する 1 つの使用例 2 番目のテーブル結果セットを返したくない場合です。

Martin Smith からのクエリに従って更新:

以下のクエリを実行して、2 番目のテーブルに参照が存在する最初のテーブルから行を取得する最も効果的な方法を見つけました。

SELECT DISTINCT c.*
FROM Customers c
JOIN Orders o ON o.custid = c.custid   

SELECT c.*
FROM Customers c
INNER JOIN (SELECT DISTINCT custid FROM Orders) AS o ON o.custid = c.custid

SELECT *
FROM Customers C
WHERE EXISTS(SELECT 1 FROM Orders o WHERE o.custid = c.custid)

SELECT *
FROM Customers c
WHERE custid IN (SELECT custid FROM Orders)

上記のすべてのクエリは、2 番目の INNER JOIN を除いて同じコストを共有します 、残りは同じ計画です。

メモリー付与:
このクエリ

SELECT DISTINCT c.*
FROM Customers c
JOIN Orders o ON o.custid = c.custid 

このクエリ

SELECT c.*
FROM Customers c
INNER JOIN (SELECT DISTINCT custid FROM Orders) AS o ON o.custid = c.custid 

..

CPU 時間、読み取り:
クエリの場合:

SELECT DISTINCT c.*
FROM Customers c
JOIN Orders o ON o.custid = c.custid   

(20000 row(s) affected)
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.
Table 'Workfile'. Scan count 48, logical reads 1344, physical reads 96, read-ahead reads 1248, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Orders'. Scan count 5, logical reads 3929, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Customers'. Scan count 5, logical reads 322, 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 = 1453 ms,  elapsed time = 781 ms.

クエリの場合:

SELECT c.*
FROM Customers c
INNER JOIN (SELECT DISTINCT custid FROM Orders) AS o ON o.custid = c.custid

(20000 row(s) affected)
Table 'Customers'. Scan count 5, logical reads 322, 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.
Table 'Workfile'. 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.
Table 'Orders'. Scan count 5, logical reads 3929, 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 = 1499 ms,  elapsed time = 403 ms.