sql-server - SQL Server Profiler 写入与 RowCounts

Question

当我在 SQL Server Profiler 中测量 Writes 和 RowCounts 时，我发现一条语句（删除）报告 Writes = 26035，但 RowCounts 为 0。这怎么可能？显然，该语句正在删除行，因为它正在写入，那么为什么这些都没有计入 rowcount 列？

Answer 1

因为 rowcount 指向返回给客户端的行数。OUTPUT除非您使用该子句，否则删除不会返回任何行。

更新：==> 我站得更正测试显示，当删除不返回行时，也会设置行数。

证明：

SELECT * 
  FROM Accounts 
 WHERE Category= 'COA'  
   AND Code between 1500 and 2000 
-- 18 Reads, 0 Writes, 51 RowCount

DELETE FROM Accounts 
 WHERE Category = 'COA' 
   AND Code between 1500 and 2000
-- 22 Reads, 1 Writes, 51 RowCount

DELETE FROM Accounts
OUTPUT DELETED.* 
WHERE Category = 'COA' 
  AND Code between 2000 and 4000
-- 24 Reads, 3 Writes, 103 RowCount

在 2 个包含 500 万条记录且不删除任何记录的表上运行删除语句给我以下查询计划：

delete clust from clust, heap where clust.Key= heap.Key
-- 19854 Reads, 0 Writes, 0 RowCount

 |--Clustered Index Delete(OBJECT:([dbo].[clust].[idx_clust]), OBJECT:([dbo].[clust].[idx2_clust]))
      |--Top(ROWCOUNT est 0)
           |--Parallelism(Gather Streams)
                |--Hash Match(Right Semi Join, HASH:([dbo].[heap].[Key])=([dbo].[clust].[Key]))
                     |--Bitmap(HASH:([dbo].[heap].[Key]), DEFINE:([Bitmap1012]))
                     |    |--Parallelism(Repartition Streams, Hash Partitioning, PARTITION COLUMNS:([dbo].[heap].[Key]))
                     |         |--Stream Aggregate(GROUP BY:([dbo].[heap].[Key]))
                     |              |--Index Scan(OBJECT:([dbo].[heap].[idx_heap]), ORDERED FORWARD)
                     |--Parallelism(Repartition Streams, Hash Partitioning, PARTITION COLUMNS:([dbo].[clust].[Key]))
                         |--Index Scan(OBJECT:([dbo].[clust].[idx2_clust]),  WHERE:(PROBE([Bitmap1012],[dbo].[clust].[Key],N'[IN ROW]')) ORDERED FORWARD)

在 2 个每个 10 行的小表上运行相同的查询会得到以下结果：

delete smallclust from smallclust, smallheap where smallclust.srp_key = smallheap.common_key
-- 45 Reads, 0 Writes, 0 RowCount

 |--Table Delete(OBJECT:([dbo].[smallclust]))
      |--Top(ROWCOUNT est 0)
           |--Nested Loops(Left Semi Join, WHERE:([dbo].[smallheap].[Key]=[dbo].[smallclust].[Key]))
                |--Table Scan(OBJECT:([dbo].[smallclust]))
                |--Table Scan(OBJECT:([dbo].[smallheap]))

因此，导致写入的哈希表的假设仍然没有定论。