Paging records on SQL server using derived tables : more question

[rbg]

I did use query plans to find out more. ( Please see the thread BELOW)

I have a question on this, if someone can help me with that it will be
great.
In my SQL query that selects data from table, I have a where clause
which states :

where PermitID like @WorkType
order by WorkStart DESC

@WorkType is a input parameter to the Stored proc and its value is
'01%'

When I use the above where clause, all the Sorts in the ESTIMATED Query
Execution plan show me a COST of 28%.

However if I change the query manually to say:

where PermitID like '01%'
order by WorkStart DESC

The COST of the Sort (in ESTIMATED Query Execution plan) reduces to 2%
and at the beginning of the PLAN, there is a Bookmark Lookup which
includes the above where clause.
Whereas with the FIRST example , the BookMark Lookup in the beginning
doesn't show that where condition.

Can anyone help me better understand this anomaly?

TIA
=====================================
I am using derived tables to Page data on the SQL Server side.
I used this link as my mentor for doing paging on the SQL
Server

http://msdn2.microsoft.com/en-us/library/ms979197.aspx

I wanted to use USER PAGING, thus I used the following code:

CREATE PROCEDURE UserPaging
(
@currentPage int = 1, @pageSize int =1000
)
AS
DECLARE @Out int, @rowsToRetrieve int, @SQLSTRING nvarchar(1000)

SET @rowsToRetrieve = (@pageSize * @currentPage)

SET NOCOUNT ON
SET @SQLSTRING = N'select
CustomerID,CompanyName,ContactName,ContactTitle from
( SELECT TOP '+ CAST(@pageSize as varchar(10)) +
'CustomerId,CompanyName,ContactName,ContactTitle from
( SELECT TOP ' + CAST(@rowsToRetrieve as varchar(10)) +
'CustomerID,CompanyName,ContactName,ContactTitle FROM
( SELECT TOP ' + CAST(@rowsToRetrieve as varchar(10)) +
'CustomerID,CompanyName,ContactName,ContactTitle FROM Customers as T1
ORDER BY contactname) AS T2 ORDER BY contactname DESC ) AS T3)
As T4 ORDER BY contactname ASC'

EXEC(@SQLSTRING)
RETURN
GO

When I use this. Assume that the Total records returned by the SQL
query is 1198.Thus when I am on Page1 the above Stored Proc (SP) will
return the first 1000 records.

This works absolutely fine.
Now I am on Page2, now I need to retrieve only the remaining 198
records.But if I use the above SP, it will return the last 1000
records.So to tweak this I used the following logic to set the

@pagesize variable:
Declare @PageCount int
select @PageCount = @TotalRows/@PageSize
if @currentPage @PageCount SET @PageSize = @TotalRows%@PageSize

Since I am on Page2 the above logic will set the PageSize to 198 and
not 1000.But when I use this logic, it takes forever for the SP to
return the 198 records in a resultset.
However if the TotalRows were = 1800, and thus the PageSize=800 or
greater, this SP returns the resultset quickly enough.

Thus to get over this problem I had to use the other logic i.e. using
Application Paging (i.e. first storing the entire result set into a
Temp table, then retrieving only the required records for the PAGE)

Can anyone suggest what is wrong with my user paging logic?????
TIA...

[Erland Sommarskog]

rbg (rb*****@gmail.com) writes:

I have a question on this, if someone can help me with that it will be
great.
In my SQL query that selects data from table, I have a where clause
which states :

where PermitID like @WorkType
order by WorkStart DESC

@WorkType is a input parameter to the Stored proc and its value is
'01%'

When I use the above where clause, all the Sorts in the ESTIMATED Query
Execution plan show me a COST of 28%.

However if I change the query manually to say:

where PermitID like '01%'
order by WorkStart DESC

The COST of the Sort (in ESTIMATED Query Execution plan) reduces to 2%
and at the beginning of the PLAN, there is a Bookmark Lookup which
includes the above where clause.
Whereas with the FIRST example , the BookMark Lookup in the beginning
doesn't show that where condition.

Can anyone help me better understand this anomaly?

That WHERE clause was not in your original post. Nor does the column
name seem entirely familiar. I gather that what you posted yesterday
was a sample from an MSDN article, but it can be tricky to give accurate
answers, ir you don't post your actual code.

But some optimizer bascis: when SQL Server builds the query plan
for a stored procedure, it builds the plan for the procedure as a
whole. This means that it does not know what values that variables
will have at time for execution. The same applies to parameters, but
in this case it does at least know the input value, and uses this
value as guidance. (This is known as parameter sbiffing.)

But SQL Server does not build a query plan every time a procedure
is executed. Instead the plan is put in cache, and the cached plan
will be reused - even if the procedure is called with input values
for which the cached plan is no good.

In your case, assume the the procedure was first called with
WorkType '%01'. For this input value any index on PermitID is not
very useful, so most likely you will get a table scan instead.

On the other hand, when you hardcode a value. SQL Server have full
information, and the odds for a good plan are much better.

To test this theory, you can say:

EXEC your_sp @WorkTyoe WITH RECOMPILE

if you get a berrer plan, the problem was that you had a plan created
for a differnt value in the cache.

--
Erland Sommarskog, SQL Server MVP, es****@sommarskog.se

Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/pro...ads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinf...ons/books.mspx

[AlterEgo]

rbg,

SqlServerCentral.com has an article on paging. You will need to sign up to
get access.

http://www.sqlteam.com/item.asp?ItemID=26455

-- Bill

"rbg" <rb*****@gmail.comwrote in message
news:11**********************@s48g2000cws.googlegr oups.com...

>I did use query plans to find out more. ( Please see the thread BELOW)

I have a question on this, if someone can help me with that it will be
great.
In my SQL query that selects data from table, I have a where clause
which states :

where PermitID like @WorkType
order by WorkStart DESC

@WorkType is a input parameter to the Stored proc and its value is
'01%'

When I use the above where clause, all the Sorts in the ESTIMATED Query
Execution plan show me a COST of 28%.

However if I change the query manually to say:

where PermitID like '01%'
order by WorkStart DESC

The COST of the Sort (in ESTIMATED Query Execution plan) reduces to 2%
and at the beginning of the PLAN, there is a Bookmark Lookup which
includes the above where clause.
Whereas with the FIRST example , the BookMark Lookup in the beginning
doesn't show that where condition.

Can anyone help me better understand this anomaly?

TIA
=====================================
I am using derived tables to Page data on the SQL Server side.
I used this link as my mentor for doing paging on the SQL
Server

http://msdn2.microsoft.com/en-us/library/ms979197.aspx

I wanted to use USER PAGING, thus I used the following code:

CREATE PROCEDURE UserPaging
(
@currentPage int = 1, @pageSize int =1000
)
AS
DECLARE @Out int, @rowsToRetrieve int, @SQLSTRING nvarchar(1000)

SET @rowsToRetrieve = (@pageSize * @currentPage)

SET NOCOUNT ON
SET @SQLSTRING = N'select
CustomerID,CompanyName,ContactName,ContactTitle from
( SELECT TOP '+ CAST(@pageSize as varchar(10)) +
'CustomerId,CompanyName,ContactName,ContactTitle from
( SELECT TOP ' + CAST(@rowsToRetrieve as varchar(10)) +
'CustomerID,CompanyName,ContactName,ContactTitle FROM
( SELECT TOP ' + CAST(@rowsToRetrieve as varchar(10)) +
'CustomerID,CompanyName,ContactName,ContactTitle FROM Customers as T1
ORDER BY contactname) AS T2 ORDER BY contactname DESC ) AS T3)
As T4 ORDER BY contactname ASC'

EXEC(@SQLSTRING)
RETURN
GO

When I use this. Assume that the Total records returned by the SQL
query is 1198.Thus when I am on Page1 the above Stored Proc (SP) will
return the first 1000 records.

This works absolutely fine.
Now I am on Page2, now I need to retrieve only the remaining 198
records.But if I use the above SP, it will return the last 1000
records.So to tweak this I used the following logic to set the

@pagesize variable:
Declare @PageCount int
select @PageCount = @TotalRows/@PageSize
if @currentPage @PageCount SET @PageSize = @TotalRows%@PageSize

Since I am on Page2 the above logic will set the PageSize to 198 and
not 1000.But when I use this logic, it takes forever for the SP to
return the 198 records in a resultset.
However if the TotalRows were = 1800, and thus the PageSize=800 or
greater, this SP returns the resultset quickly enough.

Thus to get over this problem I had to use the other logic i.e. using
Application Paging (i.e. first storing the entire result set into a
Temp table, then retrieving only the required records for the PAGE)

Can anyone suggest what is wrong with my user paging logic?????
TIA...

[rbg]

You are right, I did not include the exact query since it has a whole
of joins and many where clauses in it.
I did not want to make the post very hard to read, hence I simplified
it.

In the Stored proc I am using a String variable @SQLString
varchar(2000) to hold the entire select statement, and then executing
that SQL using EXEC (@SQLString).

Thus for debugging, I used Query Analyzer, and within the Analyzer I am
using the Select statement.
So in my test I do not use any stored proc.

so one select statement says:

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate

>From PermitMain inner join tbl_Permittee

on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like '01%' ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))
and PermitteeNumber = @PermitteeNumber
and PermitMain.Boroughcode = @Boro
order by WorkStart DESC
) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC

THIS ONE RUNS FAST and RETURNS RESULTS.

The Other Select statement:

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate

>From PermitMain inner join tbl_Permittee

on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WokStart ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))

and PermitteeNumber = @PermitteeNumber

and PermitMain.Boroughcode = @Boro

order by WorkStart DESC

) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC

TAKES FOREVER to COMPLETE.

However IF I INCREASE the PAGESIZE from 600 to 800, BOTH QUERIES RETURN
RESULTS EQUALLY FAST.

Thanks for your help
On Jan 25, 5:49 pm, Erland Sommarskog <[e-mail]:

rbg ([e-mail]) writes:

I have a question on this, if someone can help me with that it will be
great.
In my SQL query that selects data from table, I have a where clause
which states :

where PermitID like @WorkType
order by WorkStart DESC

@WorkType is a input parameter to the Stored proc and its value is
'01%'

When I use the above where clause, all the Sorts in the ESTIMATED Query
Execution plan show me a COST of 28%.

However if I change the query manually to say:

where PermitID like '01%'
order by WorkStart DESC

The COST of the Sort (in ESTIMATED Query Execution plan) reduces to 2%
and at the beginning of the PLAN, there is a Bookmark Lookup which
includes the above where clause.
Whereas with the FIRST example , the BookMark Lookup in the beginning
doesn't show that where condition.

Can anyone help me better understand this anomaly?That WHERE clause was not in your original post. Nor does the column

name seem entirely familiar. I gather that what you posted yesterday
was a sample from an MSDN article, but it can be tricky to give accurate
answers, ir you don't post your actual code.

But some optimizer bascis: when SQL Server builds the query plan
for a stored procedure, it builds the plan for the procedure as a
whole. This means that it does not know what values that variables
will have at time for execution. The same applies to parameters, but
in this case it does at least know the input value, and uses this
value as guidance. (This is known as parameter sbiffing.)

But SQL Server does not build a query plan every time a procedure
is executed. Instead the plan is put in cache, and the cached plan
will be reused - even if the procedure is called with input values
for which the cached plan is no good.

In your case, assume the the procedure was first called with
WorkType '%01'. For this input value any index on PermitID is not
very useful, so most likely you will get a table scan instead.

On the other hand, when you hardcode a value. SQL Server have full
information, and the odds for a good plan are much better.

To test this theory, you can say:

EXEC your_sp @WorkTyoe WITH RECOMPILE

if you get a berrer plan, the problem was that you had a plan created
for a differnt value in the cache.

--
Erland Sommarskog, SQL Server MVP, [e-mail]

Books Online for SQL Server 2005 athttp://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books...
Books Online for SQL Server 2000 athttp://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

[rbg]

PLEASE NOTE the variable was not WokStart but WORKTYPE.

So the query that takes very long looks like this:

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate

>From PermitMain inner join tbl_Permittee

on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WorkType ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))

and PermitteeNumber = @PermitteeNumber

and PermitMain.Boroughcode = @Boro

order by WorkStart DESC

) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC
================================================== =================
On Jan 26, 8:49 am, "rbg" <[e-mail]:

You are right, I did not include the exact query since it has a whole
of joins and many where clauses in it.
I did not want to make the post very hard to read, hence I simplified
it.

In the Stored proc I am using a String variable @SQLString
varchar(2000) to hold the entire select statement, and then executing
that SQL using EXEC (@SQLString).

Thus for debugging, I used Query Analyzer, and within the Analyzer I am
using the Select statement.
So in my test I do not use any stored proc.

so one select statement says:

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate>From PermitMain inner join tbl_Permitteeon PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like '01%' ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))
and PermitteeNumber = @PermitteeNumber
and PermitMain.Boroughcode = @Boro
order by WorkStart DESC
) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC

THIS ONE RUNS FAST and RETURNS RESULTS.

The Other Select statement:

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate>From PermitMain inner join tbl_Permitteeon PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WokStart ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))

and PermitteeNumber = @PermitteeNumber

and PermitMain.Boroughcode = @Boro

order by WorkStart DESC

) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC

TAKES FOREVER to COMPLETE.

However IF I INCREASE the PAGESIZE from 600 to 800, BOTH QUERIES RETURN
RESULTS EQUALLY FAST.

Thanks for your help
On Jan 25, 5:49 pm, Erland Sommarskog <[e-mail]:

rbg ([e-mail]) writes:

I have a question on this, if someone can help me with that it will be
great.
In my SQL query that selects data from table, I have a where clause
which states :

where PermitID like @WorkType
order by WorkStart DESC

@WorkType is a input parameter to the Stored proc and its value is
'01%'

When I use the above where clause, all the Sorts in the ESTIMATED Query
Execution plan show me a COST of 28%.

However if I change the query manually to say:

where PermitID like '01%'
order by WorkStart DESC

The COST of the Sort (in ESTIMATED Query Execution plan) reduces to 2%
and at the beginning of the PLAN, there is a Bookmark Lookup which
includes the above where clause.
Whereas with the FIRST example , the BookMark Lookup in the beginning
doesn't show that where condition.

Can anyone help me better understand this anomaly?That WHERE clause was not in your original post. Nor does the column

name seem entirely familiar. I gather that what you posted yesterday
was a sample from an MSDN article, but it can be tricky to give accurate
answers, ir you don't post your actual code.

But some optimizer bascis: when SQL Server builds the query plan
for a stored procedure, it builds the plan for the procedure as a
whole. This means that it does not know what values that variables
will have at time for execution. The same applies to parameters, but
in this case it does at least know the input value, and uses this
value as guidance. (This is known as parameter sbiffing.)

But SQL Server does not build a query plan every time a procedure
is executed. Instead the plan is put in cache, and the cached plan
will be reused - even if the procedure is called with input values
for which the cached plan is no good.

In your case, assume the the procedure was first called with
WorkType '%01'. For this input value any index on PermitID is not
very useful, so most likely you will get a table scan instead.

On the other hand, when you hardcode a value. SQL Server have full
information, and the odds for a good plan are much better.

To test this theory, you can say:

EXEC your_sp @WorkTyoe WITH RECOMPILE

if you get a berrer plan, the problem was that you had a plan created
for a differnt value in the cache.

--
Erland Sommarskog, SQL Server MVP, [e-mail]

Books Online for SQL Server 2005 athttp://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books...
Books Online for SQL Server 2000 athttp://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

[Erland Sommarskog]

rbg (rb*****@gmail.com) writes:

In the Stored proc I am using a String variable @SQLString
varchar(2000) to hold the entire select statement, and then executing
that SQL using EXEC (@SQLString).

Thus for debugging, I used Query Analyzer, and within the Analyzer I am
using the Select statement.
So in my test I do not use any stored proc.

so one select statement says:
...

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate

>>From PermitMain inner join tbl_Permittee

on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WokStart ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))
and PermitteeNumber = @PermitteeNumber
and PermitMain.Boroughcode = @Boro
order by WorkStart DESC
) as T2 order by WorkStart ASC
) as T3
) as T4 order by WorkStart DESC

TAKES FOREVER to COMPLETE.

Yes, but how does those variables makes into the dynamic SQL? You said
that you were using EXEC(), and EXEC() does not permit you to pass
parameters. Does your complete SQL string look something like:

DECLARE @Workstart, ...

SELECT @Workstart = '01%'
...
SEKECT * ....

Then you have preclsely the problem that I discussed in my previous
post. The optimizer has no clue of value @workstart has, and will make
a blind assumption.

But you should not use EXEC(). Use sp_executesql instead. sp_executesql
permits you to pass parameters, and in this case the optimizer will
be able to use be parameter values for guidance.

See http://www.sommarskog.se/dynamic_sql.html#sp_executesql for
more details on sp_excecutsql.

If you want further help, please post your entire SQL batch, that is
the one that builds the dynamic SQL. It's a bit frustrating having to
guess what you are doing - and you get better answers that way.

--
Erland Sommarskog, SQL Server MVP, es****@sommarskog.se

Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/pro...ads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinf...ons/books.mspx

[rbg]

Please find attached the complete query:

Declare @WorkType varchar(3), @PermitteeNumber varchar(5), @Boro
varchar(1)
Declare @IssueDateFrom datetime, @IssueDateTo datetime
Declare @SortExpression varchar(50), @SortOrder varchar(5)
Declare @PageNum int, @PageSize int

select @PageNum = 2, @PageSize = 1000
Declare @rowsToRetrieve int
Declare @SortOrderMirror varchar(4)

if @SortOrder = 'ASC'
SET @SortOrderMirror = 'DESC'
else
SET @SortOrderMirror = 'ASC'

SET @rowsToRetrieve = @PageNum * @PageSize

Declare @TotalRows int

SET @TotalRows = 1600

SET @PageSize = @TotalRows%@PageSize

select @WorkType = '01%', @PermitteeNumber = '00180', @Boro = 'M'
select @IssueDateFrom = '01/24/2001', @IssueDateTo = '01/24/2007'
select @SortExpression = 'WorkStart', @SortOrder = 'DESC'

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate

>From PermitMain inner join tbl_Permittee

on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WorkType ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))

and PermitteeNumber = @PermitteeNumber

and PermitMain.Boroughcode = @Boro

order by WorkStart DESC

) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC
================================================== =====================
=
if I replace the above where clause from PermitType_ID like
@WorkType to PermitType_ID like '01%'
The results are returned within 30 secs, else it takes forever.

Any Help will be grately appreciated.

TIA..
================================================== =====================
=
On Jan 26, 5:50 pm, Erland Sommarskog <[e-mail]:

rbg ([e-mail]) writes:

In the Stored proc I am using a String variable @SQLString
varchar(2000) to hold the entire select statement, and then executing
that SQL using EXEC (@SQLString).

Thus for debugging, I used Query Analyzer, and within the Analyzer I am
using the Select statement.
So in my test I do not use any stored proc.

so one select statement says:
...

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate

>From PermitMain inner join tbl_Permittee

on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WokStart ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))
and PermitteeNumber = @PermitteeNumber
and PermitMain.Boroughcode = @Boro
order by WorkStart DESC
) as T2 order by WorkStart ASC
) as T3
) as T4 order by WorkStart DESC

TAKES FOREVER to COMPLETE.Yes, but how does those variables makes into the dynamic SQL? You said

that you were using EXEC(), and EXEC() does not permit you to pass
parameters. Does your complete SQL string look something like:

DECLARE @Workstart, ...

SELECT @Workstart = '01%'
...
SEKECT * ....

Then you have preclsely the problem that I discussed in my previous
post. The optimizer has no clue of value @workstart has, and will make
a blind assumption.

But you should not use EXEC(). Use sp_executesql instead. sp_executesql
permits you to pass parameters, and in this case the optimizer will
be able to use be parameter values for guidance.

Seehttp://www.sommarskog.se/dynamic_sql.html#sp_executesqlfor
more details on sp_excecutsql.

If you want further help, please post your entire SQL batch, that is
the one that builds the dynamic SQL. It's a bit frustrating having to
guess what you are doing - and you get better answers that way.

--
Erland Sommarskog, SQL Server MVP, [e-mail]

Books Online for SQL Server 2005 athttp://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books...
Books Online for SQL Server 2000 athttp://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

[rbg]

Erland,

You were very much right regarding using sp_executesql stored proc for
executing dynamic queries.

Once I started using this:
Declare @Params nvarchar(200)
SET @Params = '@WorkTypeSQL nvarchar(3), @PermitteeNumberSQL
nvarchar(5), @BoroSQL nvarchar(1)
exec sp_executesql @Params, @WorkType, @PermitteeNumber, @Boro

The performance improved and solved my original problem.

I have one more question though.
When I used Temp tables instead of derived tables, my performance
improved significantly. The query which takes 30 seconds using the
derived tables, takes only 11 seconds when using Temp tables.

So is it better to choose the Temp table solution over the derived
tables solution?

TIA

On Jan 29, 9:02 am, "rbg" <[e-mail]:

Please find attached the complete query:

Declare @WorkType varchar(3), @PermitteeNumber varchar(5), @Boro
varchar(1)
Declare @IssueDateFrom datetime, @IssueDateTo datetime
Declare @SortExpression varchar(50), @SortOrder varchar(5)
Declare @PageNum int, @PageSize int

select @PageNum = 2, @PageSize = 1000
Declare @rowsToRetrieve int
Declare @SortOrderMirror varchar(4)

if @SortOrder = 'ASC'
SET @SortOrderMirror = 'DESC'
else
SET @SortOrderMirror = 'ASC'

SET @rowsToRetrieve = @PageNum * @PageSize

Declare @TotalRows int

SET @TotalRows = 1600

SET @PageSize = @TotalRows%@PageSize

select @WorkType = '01%', @PermitteeNumber = '00180', @Boro = 'M'
select @IssueDateFrom = '01/24/2001', @IssueDateTo = '01/24/2007'
select @SortExpression = 'WorkStart', @SortOrder = 'DESC'

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate>From PermitMain inner join tbl_Permitteeon PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WorkType ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))

and PermitteeNumber = @PermitteeNumber

and PermitMain.Boroughcode = @Boro

order by WorkStart DESC

) as T2 order by WorkStart ASC

) as T3

) as T4 order by WorkStart DESC
================================================== =====================
=
if I replace the above where clause from PermitType_ID like
@WorkType to PermitType_ID like '01%'
The results are returned within 30 secs, else it takes forever.

Any Help will be grately appreciated.

TIA..
================================================== =====================
=
On Jan 26, 5:50 pm, Erland Sommarskog <[e-mail]:

rbg ([e-mail]) writes:

In the Stored proc I am using a String variable @SQLString
varchar(2000) to hold the entire select statement, and then executing
that SQL using EXEC (@SQLString).

Thus for debugging, I used Query Analyzer, and within the Analyzer I am
using the Select statement.
So in my test I do not use any stored proc.

so one select statement says:
>...

Select * from ( Select Top 600 * from
( Select Top 2000 * from
( Select Top 2000 PermitNumber, HouseNumber, OnStreetName,
FromStreetName, ToStreetName, WorkStartDate as "WorkStart",
tbl_Permittee.Permittee_name as PermitteeName, PermitteeNumber,
PermitType_ID as "Type",
InspectionDistrict,
PermitStatus,
IssueDate
>>From PermitMain inner join tbl_Permittee
on PermitMain.PermitteeNumber = tbl_Permittee.Permittee_Number
and (tbl_Permittee.Permittee_name_flag = 'd' or
tbl_Permittee.Permittee_name_flag = 'p')
where
(PermitType_ID like @WokStart ) and worktypeid is null
and ((IssueDate between @IssueDateFrom and @IssueDateTo) or
(EmergIssueDate between @IssueDateFrom and @IssueDateTo))
and PermitteeNumber = @PermitteeNumber
and PermitMain.Boroughcode = @Boro
order by WorkStart DESC
) as T2 order by WorkStart ASC
) as T3
) as T4 order by WorkStart DESC

TAKES FOREVER to COMPLETE.Yes, but how does those variables makes into the dynamic SQL? You said

that you were using EXEC(), and EXEC() does not permit you to pass
parameters. Does your complete SQL string look something like:

DECLARE @Workstart, ...

SELECT @Workstart = '01%'
...
SEKECT * ....

Then you have preclsely the problem that I discussed in my previous
post. The optimizer has no clue of value @workstart has, and will make
a blind assumption.

But you should not use EXEC(). Use sp_executesql instead. sp_executesql
permits you to pass parameters, and in this case the optimizer will
be able to use be parameter values for guidance.

Seehttp://www.sommarskog.se/dynamic_sql.html#sp_executesqlfor
more details on sp_excecutsql.

If you want further help, please post your entire SQL batch, that is
the one that builds the dynamic SQL. It's a bit frustrating having to
guess what you are doing - and you get better answers that way.

--
Erland Sommarskog, SQL Server MVP, [e-mail]

Books Online for SQL Server 2005 athttp://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books...
Books Online for SQL Server 2000 athttp://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

[Erland Sommarskog]

rbg (rb*****@gmail.com) writes:

I have one more question though.
When I used Temp tables instead of derived tables, my performance
improved significantly. The query which takes 30 seconds using the
derived tables, takes only 11 seconds when using Temp tables.

So is it better to choose the Temp table solution over the derived
tables solution?

So instead of the derived tables, you did the SELECT TOP into the
temp tables? Or did you use the temp tables in any other way?

Assuming the first, this is one of those hairy questions of which the
short answer is "it depends". In most cases, it's more effecient to do
all in one query, rather than matierialising the intermediate results
in a temp table. This is because the optimizer may find ways to recast
the computation order without affecting the final result. But there are
always exceptions. In this particular case, the optimizer may not have
been able to find a shortcut. On the other hand, the temp table has
statistics, so when coming to the next query, the optimizer has more
information and may find a better plan.

I'm glad to hear that sp_executesql resolved your problems!

--
Erland Sommarskog, SQL Server MVP, es****@sommarskog.se

Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/pro...ads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinf...ons/books.mspx