[英]SQL Server 2008 R2: Tuning query
我有下表有10億條記錄。
create table PfTest
(
cola int,
colb int,
colc date,
cold varchar(10),
ID int
);
現在我想顯示特定日期而不是特定日期的記錄。
我正在使用以下兩種類型的查詢:
查詢1:
select DISTINCT cola, colb, colc, cold, ID
from PfTest
WHERE colc In ('2014-01-01')
AND cold NOT IN (SELECT cold
FROM PfTest
WHERE ID = 1
AND colc IN ('2014-01-02', '2014-01-03',
'2014-01-04', '2014-01-05', '2014-01-06'));
查詢2:
WITH cte AS
(
SELECT DISTINCT cola, colb, colc, cold, ID
FROM PfTest
WHERE cold NOT IN (SELECT cold FROM PfTest
WHERE ID = 1
AND colc IN('2014-01-02', '2014-01-03',
'2014-01-04', '2014-01-05', '2014-01-06'))
)
SELECT cola, colb, colc, cold, ID
FROM cte
WHERE colc IN ('2014-01-01');
以上兩個查詢計划都是相同的執行。 兩者都需要花費大量時間來執行。 我可以為這種情況寫一些更好的查詢嗎?
這是您的查詢,沒有DISTINCT
(這似乎是不必要的):
select cola, colb, colc, cold, ID
from PfTest
WHERE colc In ('2014-01-01') AND
cold NOT IN (SELECT cold
from PfTest
WHERE ID = 1 AND
colc IN ('2014-01-02', '2014-01-03', '2014-01-04', '2014-01-05', '2014-01-06')
);
我會從索引開始。 PFTest(colc, cold)
和PFTest(id, colc, cold)
。
如果子查詢返回大量數據 - 比如數百萬行 - 那么這可能是您最好使用臨時表的情況。 我會先嘗試索引。 如果這不起作用,那么帶有cold
索引的臨時表可能會起作用。 此外,雖然它對性能影響不大,但我會使用NOT EXISTS
而不是NOT IN
來表達查詢:
select cola, colb, colc, cold, ID
from PfTest t
WHERE colc In ('2014-01-01') AND
NOT EXISTS (SELECT 1
from PfTest t2
WHERE t2.cold = t1.cold AND t2.ID = 1 AND
t2.colc IN ('2014-01-02', '2014-01-03', '2014-01-04', '2014-01-05', '2014-01-06')
);
對於此版本,最佳索引是PfTest(cold, id, colc)
。
當匹配列具有NULL
值時, NOT EXISTS
具有更直觀的行為。
首先
select DISTINCT cola, colb, colc, cold, ID from PfTest WHERE colc In ('2014-01-01') AND cold NOT IN (SELECT cold FROM PfTest WHERE ID = 1 AND colc IN ('2014-01-02', '2014-01-03', '2014-01-04', '2014-01-05', '2014-01-06'));
和...一樣
select DISTINCT cola, colb, colc, cold, ID from PfTest WHERE colc In ('2014-01-01') AND colc NOT IN ('2014-01-02', '2014-01-03', '2014-01-04', '2014-01-05', '2014-01-06')
AND NOT(ID = 1);
因為內表和外表是相同的。
由於您不想一次又一次地重復使用表(因為它占用了十億行),因此將數據提取到臨時表是一種更好的做法。 然后在其上創建合適的索引。
select cola, colb, colc, cold, ID INTO #PfTest FROM PfTest CREATE NONCLUSTERED INDEX IX_PFTEST1 ON #PfTest(id) INCLUDE (cola, colb, colc, cold) CREATE NONCLUSTERED INDEX IX_PFTEST2 ON #PfTest(colc) INCLUDE (cola, colb, id, cold) CREATE NONCLUSTERED INDEX IX_PFTEST3 ON #PfTest(cold) INCLUDE (cola, colb, id, colc) select cola, colb, colc, cold, ID from #PfTest WHERE colc In ('2014-01-01') INTERSECT select cola, colb, colc, cold, id from (select cola, colb, colc, cold, ID from #PfTest EXCEPT SELECT cola, colb, colc, cold, 1 id FROM #PfTest where colc IN('2014-01-02', '2014-01-03', '2014-01-04', '2014-01-05', '2014-01-06'))A
使用EXCEPT
代替NOT IN
來改善性能。
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