Selecting only one row at a time

Hi experts,
i have following doubt regarding selecting rows from a db:
Is there any way of selecting only one row AT A TIME from a dabase just to collect the data in rows instead of in a unique document containing all the rows?
I would like you to ellaborate on this as i need to send only one row to the IE, and then other row, and so on... without throwing any error!
I have seen that there are SELECT SINGLE and SELECT UP TO 1 ROW, but these two methods are only useful when retrieving only one row, and that does not match my requirements. I need to process all the rows but one by one..
I know that we can use the receiver jdbc adapter as if it was a sender by means of its specific datatype, but how to do it row by row??
Hope i had explained well..
Thanks in advance and best regards,
David

Hi kiran,
Yes, my table has 5 not null fields but i am selecting and updating fixes values so i think that I will definetely go for the next solution:
SELECT * FROM t1 WHERE status='0' and ROWNUM<2;
UPDATE t1 SET status='1' WHERE status='0' and ROWNUM<2;
My only concern is if the update will take the same row that the select.... BTW, I think it will
..What do you guys think?
I ve been trying to operate with your proposed queries but i received some errors. Your queries are very interesting but i think that with the above ones i meet my requirements as the status field will be 0 for not processed rows and 1 for precessed ones (and the update will look for the row that meets the same 'where' clause than the select, and then, and only then, it will set status='1').
The only thing i have to care about is what i questioned before.
Thanks a lot and best regards,
David

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Please can help me someone.
Thanks.
Bianca

mxallen wrote:
Bianca,
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I looks to me that you count is the number of rows in the entire table "main_pages"
while you select is for the data in the "subject" column only.
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Matt
WHAATT?
What do you mean by "just one row in that subject column"?
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I can select only one row in my table why?

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write a TreeSelectionListener which knows all Trees in your application. add the listener to all three Trees. within the valueChanged method, check the events source to evaluate the tree, which fired the event. close all selections of all trees ( method clearSelection() ) except the one, which fired the event.
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Edited by: 963214 on Oct 5, 2012 10:12 AM
Edited by: 963214 on Oct 5, 2012 10:40 AM

try this... hope this helps...
with xx as(
select '1' as aid,'john' as anm from dual union all
select '2' as aid,'mary' as anm from dual union all
select '3' as aid,'alvin' as anm from dual union all
select '4' as aid,'trevor' as anm from dual union all
select '5' as aid,'jess' as anm from dual
), yy as(
select '1' aid from dual union all
select '2' aid from dual union all
select '2' aid from dual union all
select '3' aid from dual union all
select '3' aid from dual union all
select '3' aid from dual union all
select '4' aid from dual union all
select '4' aid from dual union all
select '4' aid from dual union all
select '4' aid from dual union all
select '4' aid from dual union all
select '5' aid from dual
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(SELECT a.anm as nm, COUNT(t.aid) AS worksold
FROM xx a, yy t
WHERE a.aid = t.aid
GROUP BY anm
order by worksold desc) x
where rownum = 1; gives
trevor 5In 2 ^nd^ table, i've considered only 1 column which is actually used. Rest columns are unessential.
Ranit B.
Edited by: ranit B on Oct 6, 2012 12:20 AM

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Hi Sascha,
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any other suggestions?
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I have developed a table in which I am using Selection Listener to perform some task when any row is selected.
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Hi,
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Select Single * and Select upto one row

Hi all,
Can anybody tell me what is difference between Select single * and select upto one row?
And which one is better?
Thanks in advance.......

According to SAP Performance course the SELECT UP TO 1 ROWS is faster than SELECT SINGLE because you are not using all the primary key fields.
select single is a construct designed to read database records with primary key. In the absence of the primary key, it might end up doing a sequential search, whereas the select up to 1 rows may assume that there is no primary key supplied and will try to find most suitable index.
The best way to find out is through sql trace or runtime analysis.
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The System test result showed that the variant Single * takes less time than Up to 1 rows as there is an additional level for COUNT STOP KEY for SELECT ENDSELECT UP TO 1 ROWS.
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Mainly: to read data from
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UTO 1 rows will get the list of the records for the given match and iwll show the first record from the list.So it will take time to get the record.
SELECT SINGLE VBELN from VBAK
where MATNR = '1M20'.
---Thjis will get the first matched record and will display the record
SELECT VBELN from VBAK
where MATNR = '1M20' upto 1 rows.
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The Major difference between Select Single and Select UPTO 1 rows is The Usage Of Buffer for each.
Select Single will search for all the satisfied data and bring all that data into Buffer and later it will give to that data to the program.
Select UPTO 1 Rows will end the search after getting the 1st satisfied record and gives that record to the program.
Thus Select Single will take much processing time when compare with Select UPTO 1 rows.
Also
check these threads..
Difference between Select Single and Selct upto 1 row
Difference between Select Single and Select upto 1 row
Difference between select single and select upto one row
Difference between 'select single *' and 'select upto 1 rows'
difference between select single and select up to 1 rows
regards,
srinivas
<b>*reward for useful answers*</b>

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This is our main database, so most of the applications access it.
The day after the migration, when users started to run tasks, the database access started to experiment a total failure.
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I converted the sample program to VB.NET:
Public Class Form1
Private mbCancel As Boolean = False
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim soConn As ADODB.Connection
Dim soRst As ADODB.Recordset
Dim sdData As Date
Dim slValue As Long
Dim slDelay As Long
'create database vbtest
'go
' CREATE TABLE [dbo].[ControlNumTest](
' [UltData] [datetime] NOT NULL,
' [UltNum] [int] NOT NULL,
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' [UltData] Asc
' )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
' ) ON [PRIMARY]
mbCancel = False
Do
' Configure the Connection object
soConn = New ADODB.Connection
With soConn
.ConnectionString = "Provider=SQLNCLI11;Initial Catalog=vbtest;Data Source=localhost;trusted_connection=yes"
.IsolationLevel = ADODB.IsolationLevelEnum.adXactCursorStability
.Mode = ADODB.ConnectModeEnum.adModeReadWrite
.CursorLocation = ADODB.CursorLocationEnum.adUseServer
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Call soConn.BeginTrans()
' Configure the RecordSet object
soRst = New ADODB.Recordset
With soRst
.ActiveConnection = soConn
.CursorLocation = ADODB.CursorLocationEnum.adUseServer
.CursorType = ADODB.CursorTypeEnum.adOpenForwardOnly
.LockType = ADODB.LockTypeEnum.adLockPessimistic
.Open("SELECT * FROM dbo.ControlNumTest")
End With
With soRst
sdData = .Fields!UltData.Value ' Read the last Date (LOCK INFO 1: See comments bello
slValue = .Fields!UltNum.Value ' Read the last Number
If sdData <> Date.Now.Date Then ' Date has changed?
sdData = Date.Now.Date
slValue = 1 ' Restart number
End If
.Fields!UltData.Value = sdData ' Update data
.Fields!UltNum.Value = slValue + 1 ' Next number
End With
Call soRst.Update()
Call soRst.Close()
' Ends the transaction
Call soConn.CommitTrans()
Call soConn.Close()
soRst = Nothing
soConn = Nothing
txtUltNum.Text = slValue + 1 ' Display the last number
Application.DoEvents()
slDelay = Int(((Rnd * 250) + 100) / 100) * 100
System.Threading.Thread.Sleep(slDelay)
Loop While mbCancel = False
If mbCancel = True Then
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End If
Exit Sub
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
mbCancel = True
End Sub
End Class
And created the table
CREATE TABLE [dbo].[ControlNumTest](
[UltData] [datetime] NOT NULL,
[UltNum] [int] NOT NULL,
CONSTRAINT [PK_CorreioNumTeste] PRIMARY KEY CLUSTERED
[UltData] Asc
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = on, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY]
go insert into ControlNumTest values (cast(getdate()as date),1)
Then ran 3 copies of the program and generated the deadlock:
<deadlock>
<victim-list>
<victimProcess id="processf27b1498" />
</victim-list>
<process-list>
<process id="processf27b1498" taskpriority="0" logused="0" waitresource="KEY: 35:72057594039042048 (a01df6b954ad)" waittime="1970" ownerId="3181" transactionname="implicit_transaction" lasttranstarted="2014-02-14T15:49:31.263" XDES="0xf04da3a8" lockMode="X" schedulerid="4" kpid="9700" status="suspended" spid="51" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2014-02-14T15:49:31.267" lastbatchcompleted="2014-02-14T15:49:31.267" lastattention="1900-01-01T00:00:00.267" clientapp="vbt" hostname="DBROWNE2" hostpid="21152" loginname="NORTHAMERICA\dbrowne" isolationlevel="read committed (2)" xactid="3181" currentdb="35" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128058">
<executionStack>
<frame procname="adhoc" line="1" stmtstart="80" sqlhandle="0x020000008376181f3ad0ea908fe9d8593f2e3ced9882f5c90000000000000000000000000000000000000000">
UPDATE [dbo].[ControlNumTest] SET [UltData]=@Param000004,[UltNum]=@Param000005 </frame>
<frame procname="unknown" line="1" sqlhandle="0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000">
unknown </frame>
</executionStack>
<inputbuf>
(@Param000004 datetime,@Param000005 int)UPDATE [dbo].[ControlNumTest] SET [UltData]=@Param000004,[UltNum]=@Param000005 </inputbuf>
</process>
<process id="processf6ac9498" taskpriority="0" logused="10000" waitresource="KEY: 35:72057594039042048 (a01df6b954ad)" waittime="1971" schedulerid="5" kpid="30516" status="suspended" spid="55" sbid="0" ecid="0" priority="0" trancount="1" lastbatchstarted="2014-02-14T15:49:31.267" lastbatchcompleted="2014-02-14T15:49:31.267" lastattention="1900-01-01T00:00:00.267" clientapp="vbt" hostname="DBROWNE2" hostpid="27852" loginname="NORTHAMERICA\dbrowne" isolationlevel="read committed (2)" xactid="3182" currentdb="35" lockTimeout="4294967295" clientoption1="671156256" clientoption2="128058">
<executionStack>
<frame procname="adhoc" line="1" sqlhandle="0x020000003c6309232ab0edbe0a7790a816a09c4c5ac6f43c0000000000000000000000000000000000000000">
FETCH API_CURSOR0000000000000001 </frame>
<frame procname="unknown" line="1" sqlhandle="0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000">
unknown </frame>
</executionStack>
<inputbuf>
FETCH API_CURSOR0000000000000001 </inputbuf>
</process>
</process-list>
<resource-list>
<keylock hobtid="72057594039042048" dbid="35" objectname="vbtest.dbo.ControlNumTest" indexname="PK_CorreioNumTeste" id="lockff6e6c80" mode="U" associatedObjectId="72057594039042048">
<owner-list>
<owner id="processf6ac9498" mode="S" />
<owner id="processf6ac9498" mode="U" requestType="wait" />
</owner-list>
<waiter-list>
<waiter id="processf27b1498" mode="X" requestType="convert" />
</waiter-list>
</keylock>
<keylock hobtid="72057594039042048" dbid="35" objectname="vbtest.dbo.ControlNumTest" indexname="PK_CorreioNumTeste" id="lockff6e6c80" mode="U" associatedObjectId="72057594039042048">
<owner-list>
<owner id="processf27b1498" mode="U" />
<owner id="processf27b1498" mode="U" />
<owner id="processf27b1498" mode="X" requestType="convert" />
</owner-list>
<waiter-list>
<waiter id="processf6ac9498" mode="U" requestType="wait" />
</waiter-list>
</keylock>
</resource-list>
</deadlock>
It's the S lock that comes from the cursor read that's the villian here. U locks are compatible with S locks, so one session gets a U lock and another gets an S lock. But then the session with an S needs a U, and the session with a U needs an
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The right way to fix this code is to add (UPDLOCK,SERIALIZABLE) to the cursor
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So each session reads the table with a restrictive lock, and you don't mix S, U and X locks in this transaction. This resolves the deadlock, but requires a code change.
I tried several things that didn't require a code, which did not resolve the deadlock;
1) setting ALLOW_ROW_LOCKS=OFF ALLOW_PAGE_LOCKS=OFF
2) SERIALIZABLE isolation level
3) Switching OleDB providers from SQLOLEDB to SQLNCLI11
Then I replaced the table with a view containing a lock hint:
CREATE TABLE [dbo].[ControlNumTest_t](
[UltData] [datetime] NOT NULL,
[UltNum] [int] NOT NULL,
CONSTRAINT [PK_CorreioNumTeste] PRIMARY KEY CLUSTERED
[UltData] Asc
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = on, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY]
go
create view ControlNumTest as
select * from ControlNumTest_t with (tablockx)
Which, at least in my limited testing, resovlved the deadlock without any client code change.
David
David http://blogs.msdn.com/b/dbrowne/

Diffrence b/w select single & select upto one row

hi
wat is the diffrence b/w select single & select upto one row?
deepak

Hi,
Select single has to be used with a where condition that has all the key fields:
It will always return a unique record(If a match is found).
Select upto 1 rows would get your the first record if multiple matches are found.
and select up to has to be end with endselect statements.
According to SAP Performance course the SELECT UP TO 1 ROWS is faster than SELECT SINGLE because you are not using all the primary key fields.
select single is a construct designed to read database records with primary key. In the absence of the primary key, it might end up doing a sequential search, whereas the select up to 1 rows may assume that there is no primary key supplied and will try to find most suitable index.
The best way to find out is through sql trace or runtime analysis.
Use "select up to 1 rows" only if you are sure that all the records returned will have the same value for the field(s) you are interested in. If not, you will be reading only the first record which matches the criteria, but may be the second or the third record has the value you are looking for.
The System test result showed that the variant Single * takes less time than Up to 1 rows as there is an additional level for COUNT STOP KEY for SELECT ENDSELECT UP TO 1 ROWS.
The 'SELECT SINGLE' statement selects the first row in the database that it finds that fulfils the 'WHERE' clause If this results in multiple records then only the first one will be returned and therefore may not be unique.
Mainly: to read data from
The 'SELECT .... UP TO 1 ROWS' statement is subtly different. The database selects all of the relevant records that are defined by the WHERE clause, applies any aggregate, ordering or grouping functions to them and then returns the first record of the result set.
Mainly: to check if entries exist.
When you say SELECT SINGLE, it means that you are expecting only one row to be present in the database for the condition you're going to specify in the WHERE clause. so that means, you will have to specify the primary key in your WHERE clause. Otherwise you get a warning.
SELECT UP TO 1 ROWS is used in cases where you just want to make sure that there is at least one entry in the database table which satisfies your WHERE clause. Generally, it is meant to be used for existence-check.
You may not want to really use the values returned by the SELECT statement in this case (thought this may not necessarily be so).And in each case the database optimizer may choose a different strategy to retrieve the data.
Knowing when to use SELECT SINGLE or SELECT ... UP TO 1 ROWS
A lot of people use the SELECT SINGLE statement to check for the existence of a value in a database. Other people prefer to use the 'UP TO 1 ROWS' variant of the SELECT statement.
So what's the difference between using 'SELECT SINGLE' statement as against a 'SELECT .... UP TO 1 ROWS' statement ?
If you're considering the statements
SELECT SINGLE field INTO w_field FROM table.
and
SELECT field INTO w_field FROM table UP TO 1 ROWS. ENDSELECT.
then looking at the result, not much apart from the extra ENDSELECT statement. Look at the run time and memory usage and they may be worlds apart.
Why is this ?? The answer is simple.
The 'SELECT SINGLE' statement selects the first row in the database that it finds that fulfils the 'WHERE' clause If this results in multiple records then only the first one will be returned and therefore may not be unique.
The 'SELECT .... UP TO 1 ROWS' statement is subtly different. The database selects all of the relevant records that are defined by the WHERE clause, applies any aggregate, ordering or grouping functions to them and then returns the first record of the result set.
According to SAP Performance course the SELECT UP TO 1 ROWS is faster than SELECT SINGLE because you are not using all the primary key fields.
http://sap-img.com/abap/difference-between-select-single-and-select-upto-one-rows.htm
Check these links -
The specified item was not found.
diff between select single and up to one row
diff b/w SECELT SINGLE * AND SELECT UPTO ONE ROW
Regards,
Priyanka.

Diff bw select single * and select upto one row

hai,
what is the difference between select single * and select upto one row.

hi,
ex code
Report Z_Difference
Message-id 38
Line-Size 80
Line-Count 0
No Standard Page Heading.
Start-Of-Selection.
Data: w_Single type Posnr,
t_Rows type standard table of Posnr
initial size 0
with header line.
Select single Posnr
from zDifference
into w_Single.
Select Posnr
into table t_Rows
from zDifference
up to 1 rows
order by Posnr descending.
Write :/ 'Select single:', w_Single.
Skip 1.
Write :/ 'Up to 1 rows :'.
Loop at t_Rows.
Write t_Rows.
EndLoop.
According to SAP Performance course the SELECT UP TO 1 ROWS is faster than SELECT SINGLE because you are not
using all the primary key fields.
select single is a construct designed to read database records with primary key. In the absence of the primary key,
it might end up doing a sequential search, whereas the select up to 1 rows may assume that there is no primary key
supplied and will try to find most suitable index.
The best way to find out is through sql trace or runtime analysis.
Use "select up to 1 rows" only if you are sure that all the records returned will have the same value for the field(s)
you are interested in. If not, you will be reading only the first record which matches the criteria, but may be the
second or the third record has the value you are looking for.
The System test result showed that the variant Single * takes less time than Up to 1 rows as there is an additional
level for COUNT STOP KEY for SELECT ENDSELECT UP TO 1 ROWS.
The 'SELECT SINGLE' statement selects the first row in the database that it finds that fulfils the 'WHERE' clause
If this results in multiple records then only the first one will be returned and therefore may not be unique.
Mainly: to read data from
The 'SELECT .... UP TO 1 ROWS' statement is subtly different. The database selects all of the relevant records that
are defined by the WHERE clause, applies any aggregate, ordering or grouping functions to them and then returns
the first record of the result set.
Mainly: to check if entries exist.
You can refer to the below link..
http://www.sap-img.com/abap/difference-between-select-single-and-select-upto-one-rows.htm
rgds
anver
if hlped pls mark points

Select single * & Select * upto one row

What is the difference between Select single * & Select * upto one row?Performance wise which is a better one?

Hi,
According to SAP Performance course the SELECT UP TO 1 ROWS is faster than SELECT SINGLE because you are not using all the primary key fields.
Select single is a construct designed to read database records with primary key. In the absence of the primary key, it might end up doing a sequential search, whereas the select up to 1 rows may assume that there is no primary key supplied and will try to find most suitable index.
The best way to find out is through sql trace or runtime analysis.
Use "select up to 1 rows" only if you are sure that all the records returned will have the same value for the field(s) you are interested in. If not, you will be reading only the first record which matches the criteria, but may be the second or the third record has the value you are looking for.
The System test result showed that the variant Single * takes less time than Up to 1 rows as there is an additional level for COUNT STOP KEY for SELECT ENDSELECT UP TO 1 ROWS.
The 'SELECT SINGLE' statement selects the first row in the database that it finds that fulfils the 'WHERE' clause If this results in multiple records then only the first one will be returned and therefore may not be unique.
Mainly: to read data from
The 'SELECT .... UP TO 1 ROWS' statement is subtly different. The database selects all of the relevant records that are defined by the WHERE clause, applies any aggregate, ordering or grouping functions to them and then returns the first record of the result set.
Mainly: to check if entries exist.
Select Single
You need to mention all the key fields of the table.
No END SELECT required.
More performance compared to upto 1 row.
Where as UP to 1 row.
YOu can use if you do not have all the primiary key fields available.
END SELECT requeired.
Since all keys are not passing, possiblities of have other rows which satisfies the condition.
Select Statement with EndSelect is a loop, which in a single run retrieves a single Record. This Record has to be stored in a Work Area and then appended into an Internal Table.
Select Statements without EndSelect is not a loop and it retrieves the whole Record set matching the Criteria in a single shot and has to be Stored in an Internal Table Directly.
The most important thing to remember about the SELECT SINGLE is
There are several things to remember:
1) It retrieves only one row
2) It does not need an ENDSELECT statement
3) THE FULL KEY OF THE TABLE MUST BE INCLUDED IN
THE WHERE CLAUSE OF THE SELECT STATEMENT
Regards

Selecting only one row at a time

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