[英]how can we reduce the cost of temp table scan while feching count of records by using sql server
here just i am trying to know count of records in the temp table and passing to another variable, so that it was showing in the execution plan table scan about 100 % 在这里,我只是想知道临时表中的记录数并传递给另一个变量,因此它在执行计划表扫描中显示了大约100%
please find the below query which i was doing 请找到我正在做的以下查询
DECLARE @tmpANHdr TABLE (
hdrId INT IDENTITY,
CBFId NVARCHAR(32),
ACPT_REJ_FLAG NVARCHAR(8),
PROC_FILE_NAME NVARCHAR(50))
INSERT INTO @tmpANHdr
SELECT TOP 100 AHR_CB_FTS_FILE_ID,
AHR_ACCT_REJ_FLAG,
AHR_PROC_FILE_NAME
FROM FTS_ACK_NAK_HEADER WITH (NOLOCK)
WHERE AHR_FLAG IS NULL
OR AHR_FLAG = 0
DECLARE @varRecordCount INT
SELECT @varRecordCount = Count(1)
FROM @tmpANHdr
SET @varIndex = 1
IF( @varIndex <= @varRecordCount )
BEGIN
PRINT 'hi'
END
A scan on a table variable with no more than 100 rows is likely to be pretty cheap anyway. 无论如何,对不超过100行的表变量进行扫描可能很便宜。 The table scan operation might be costed at 100% of the plan for the statement but that is 100% of a pretty small number.
表扫描操作的费用可能是语句计划的100%,但这只是一个很小数目的100%。
You can avoid this cost entirely though by just looking at @@rowcount
after the insert as below. 您可以完全避免此费用,尽管只需在插入后查看
@@rowcount
,如下所示。
DECLARE @varRecordCount INT;
INSERT INTO @tmpANHdr
SELECT TOP 100 AHR_CB_FTS_FILE_ID,
AHR_ACCT_REJ_FLAG,
AHR_PROC_FILE_NAME
FROM FTS_ACK_NAK_HEADER WITH (NOLOCK)
WHERE AHR_FLAG IS NULL
OR AHR_FLAG = 0
SET @varRecordCount = @@ROWCOUNT
You could put a primary key (index) on the identity column and that might make it perform better: 您可以在标识列上放置一个主键(索引),这可能使其性能更好:
DECLARE @tmpANHdr TABLE (
hdrId INT IDENTITY PRIMARY KEY,
CBFId NVARCHAR(32),
ACPT_REJ_FLAG NVARCHAR(8),
PROC_FILE_NAME NVARCHAR(50))
Also, do you end up using the table variable for anything else? 此外,您最终是否将table变量用于其他用途? Why not just do this?
为什么不这样做呢?
DECLARE @varRecordCount INT
SELECT @varRecordCount = Count(TOP 100 *)
FROM FTS_ACK_NAK_HEADER WITH (NOLOCK)
WHERE AHR_FLAG IS NULL
OR AHR_FLAG = 0
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