与OVER
子句集合函数发射的实际行数可以如下所示:从表AS x INNER JOIN(选择分区列,AggregateWithoutOverClause(...)... FROM ...)AS y ON x.PartitionColumns = y.PartitionColumns(如果分区列是必需的 - NOT NULL)。
例子:
SET STATISTICS IO ON;
SET NOCOUNT ON;
-- OP's query
SELECT sal,sum(sal) over(PARTITION BY empno)
FROM emp;
-- Reqwriten query
SELECT a.sal, b.SumSal
FROM emp a
INNER JOIN (SELECT EMPNO, SUM(sal) AS SumSal FROM emp GROUP BY EMPNO) b ON a.EMPNO = b.EMPNO;
结果:
sal
----------- -----------
1 10
2 10
3 10
4 10
1 3
2 3
Table 'Worktable'. Scan count 3, logical reads 21, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'EMP'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
sal SumSal
----------- -----------
1 10
2 10
3 10
4 10
1 3
2 3
Table 'Worktable'. Scan count 3, logical reads 21, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'EMP'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
执行计划:
这仅说明了最后一个加入:
有关第一次加入的说明可在每组处理/ Partitioning and the Common Subexpression Spool的部分中找到。