[英]Query optimization in SQL Server
SELECT
T2.Entity1Id, T1.Entity1Id
FROM
T1
FULL OUTER JOIN
T2 ON T1.c2 = T2.c2 AND T1.c1 = T2.c1 AND T1.c3 = 1
WHERE
((T1.c1 = 123 ) OR (T2.c1 = 123))
AND (T1.c3 = 1 OR T1.c3 IS NULL)
Above query is taking 12 seconds in SQL Server 2014, any idea to tune the query? 上面的查询在SQL Server 2014中耗时12秒,您有什么想法可以调整查询? There are indexes on C1,C2,C3 columns.
在C1,C2,C3列上有索引。
Observation: in the above query, when I remove a condition from OR (ie 观察:在上面的查询中,当我从OR中删除条件时(即
SELECT
T2.Entity1Id, T1.Entity1Id
FROM
T1
FULL OUTER JOIN
T2 ON T1.c2 = T2.c2 AND T1.c1 = T2.c1 AND T1.c3 = 1
WHERE
(T1.c1 = 123) AND (T1.c3 = 1 OR T1.c3 IS NULL)
then it's returning results in 0 seconds. 然后在0秒内返回结果。
Each table has around 500'000 records. 每个表有大约500'000条记录。
First, the final condition (T1.c3 = 1 OR T1.c3 IS NULL)
is redundant. 首先,最终条件
(T1.c3 = 1 OR T1.c3 IS NULL)
是多余的。 Given the join
condition, these are the only possible values. 给定
join
条件,这些是唯一可能的值。 So, the query is: 因此,查询为:
SELECT T2.Entity1Id, T1.Entity1Id
FROM T1 FULL OUTER JOIN
T2
ON T1.c2 = T2.c2 AND T1.c1 = T2.c1 AND T1.c3 = 1
WHERE (T1.c1 = 123 ) OR (T2.c1 = 123)
If this doesn't have good performance, consider breaking this into two queries: 如果这样做的性能不好,请考虑将其分为两个查询:
SELECT T2.Entity1Id, T1.Entity1Id
FROM T1 LEFT JOIN
T2
ON T1.c2 = T2.c2 AND T1.c1 = T2.c1 AND T1.c3 = 1
WHERE T1.c1 = 123
UNION
SELECT T2.Entity1Id, T1.Entity1Id
FROM T2 LEFT JOIN
T1
ON T1.c2 = T2.c2 AND T1.c1 = T2.c1 AND T1.c3 = 1
WHERE T2.c1 = 123
Sometimes, the optimization of the separate subqueries is much better than the optimization for the full outer join
. 有时,单独子查询的优化要比
full outer join
的优化好得多。
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