[英]SQL Server 2008 R2: Tuning query
我有下表有10亿条记录。
create table PfTest
(
cola int,
colb int,
colc date,
cold varchar(10),
ID int
);
现在我想显示特定日期而不是特定日期的记录。
我正在使用以下两种类型的查询:
查询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'));
查询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');
以上两个查询计划都是相同的执行。 两者都需要花费大量时间来执行。 我可以为这种情况写一些更好的查询吗?
这是您的查询,没有DISTINCT
(这似乎是不必要的):
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')
);
我会从索引开始。 PFTest(colc, cold)
和PFTest(id, colc, cold)
。
如果子查询返回大量数据 - 比如数百万行 - 那么这可能是您最好使用临时表的情况。 我会先尝试索引。 如果这不起作用,那么带有cold
索引的临时表可能会起作用。 此外,虽然它对性能影响不大,但我会使用NOT EXISTS
而不是NOT IN
来表达查询:
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')
);
对于此版本,最佳索引是PfTest(cold, id, colc)
。
当匹配列具有NULL
值时, NOT EXISTS
具有更直观的行为。
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...一样
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);
因为内表和外表是相同的。
由于您不想一次又一次地重复使用表(因为它占用了十亿行),因此将数据提取到临时表是一种更好的做法。 然后在其上创建合适的索引。
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
来改善性能。
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