topic Re: select upto 1 row & select single * in Application Development and Automation Discussions

select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:30:11 GMT

what is the differece b/t select upto 1 row and select single *.

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:33:41 GMT

Difference is select upto 1 row will select all the records in that condition and then does some grouping or sorting and then outputs the record. Takes more time.

But select single selects the forst row which meets that condition and gives the result.

For more details check blogs there is an article.

Keyword Performance tuning.

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:33:43 GMT

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.

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.

Best regards,

Prashant

PS : Please award points for all helpful answers

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:36:18 GMT

for single select you must know the primary key.for up to no need to know primary keys..

with regards

srini Kumar

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:37:40 GMT

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.

Also have a look at:

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:42:47 GMT

Hi,

This question is very well answered in ABAP FAQ.

Refer

https://www.sdn.sap.com/irj/sdn/developerareas/abap?rid=/library/uuid/840ad679-0601-0010-cd8e-9989fd650822

here is the explanation...

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.

Get the difference ??

If not, here is a good example, credit for this example goes to Richard Harper, a friend of mine on sapfans.com :

Create a Ztable called ZDifference with 2 fields in it, MANDT of type MANDT and POSNR of type POSNR. Make sure both of these are keys. Also create a table maintenance dialog for it (SE11->Utilities->Table Maintenance Generator). Fill the table with ten rows 000001-000010.

Then run the program shown below:

Code:

Program: Z_Difference
Purpose: A program that demonstrates the difference
between SELECT SINGLE and SELECT UP TO n ROWS.
This program requires the data table Z_DIFFERENCE
to have been created according to the structure
outlined in the text above and populated with
at least 10 records.
Creation Date: 21/04/2004
Requested By:
Reference Doc:
Author: R Harper
Modification History:
Date Reason Transport Who

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.

You should see the output:

Select single: 000001

Up to 1 rows : 000010

The first 'SELECT' statement selected the first record in the database according to any selection criterion in the 'WHERE' clause. This is what a 'SELECT SINGLE' does. The second 'SELECT' has asked the database to reverse the order of the records before returning the first row of the result.

In order to be able to do this the database has read the entire table, sort it and then return the first record. If there was no ORDER BY clause then the results would have been identical (ie both '000001') but the second select if given a big enough table to look at would be far slower.

Note that this causes a problem in the Extended Program Check if the full key is not specified in a 'SELECT SINGLE'. Replacing the 'SELECT SINGLE' by an "UP TO 1 ROWS" will give the same exact results without any warning but the program will run slower and consume more memory. This is a good example of a warning that we should ignore... considering you are sure of what you are doing !!

Regards,

Tanveer.

<b>Please mark helpful answers</b>

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:44:05 GMT

Hi,

please check this thread.

if you use select single you need to give all keys in where clause, but in case of select up to 1 rows you can do with out primary keys..

Regards

vijay

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 04:45:49 GMT

Hi,

Go through the below link:

http://www.sap-basis-abap.com/abap/difference-between-select-single-and-up-to-1-row.htm

Hope this will helpful.

Regards,

Bhavana

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 05:03:30 GMT

Select single satement

>and select up to one row

select gives u a stack of records...with single u get the last row of stack and with upto 1 rows u get the first row...so if u use select upto 1 rows the select doesnot fetch a stack but gets the first row and leaves...got it !!

Regards

Niraj Kumar

Patni Computers Systems

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 05:03:32 GMT

hi,

if u r using select single u hv to give all primary keys in where clause.

but if u r using select upto 1 row there is no need to give primary key in where clause.

naveen.

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 09:18:12 GMT

Hai

Check the following Differences

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.

The best way to find out is through sql trace or runtime analysis.

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.

Mainly: to read data from

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

Regards

Sreeni

Re: select upto 1 row & select single *

Former Member — Mon, 17 Jul 2006 14:12:50 GMT

Hi,

Difference is very simple...

Whenever you query table with full primary key use 'Select single *...with full primary key"

If you do not have primary key while selecting data from table it is better to user Select upto 1 rows, which returns you first record which satisfy your where clause from table ...which is much faster if you do not have primary key...

Cheers,

Nilesh