On what basis sql server sorts the rows

Hi,

When I execute the following statement:

Select * from table1;

On what basis, SQL server decides the sequence of these rows?

I need to fetch data from a table with very large number of rows. Because of the datasize I need to do this in chunks. I am thinking of passing row counter and fetch N rows at a time. I want to know if there is a need for sorting a table before I apply the above logic or I can rely on default sorting.

Thanks veyr much.

Regards,

Tim

hi Tim,

you always have to provide a sort (ORDER BY) as the engine can return data in no actual order at all.. data is scanned with IO operations that are not limited to a "physical matter", so, without an ORDER BY clause, they are returned in the order they are read.. if you have a multi cpu machine, different processors can get data in "whatever order" and merged in the actual results... usually the "physical order" of a clustered table (a table with a clustered index) is used, but, again, that order is not guaranteed.. if you need (as you usually do) a particular order, whatever it could be, you have to provide that "hint" to the query processor... this is even more "important" if you have to do it in chunck (where you should use the ROW_NUMBER() OVER( ORDER BY orderCol) new clause of SQL Server 2005).. this obviously makes the query "heavier", as the result must be first generated and then ordered, but gives you the "real" taste of correct data and not data found over again and again in the successive calls..

remember that the ORDER BY clause is "cursor clause" and not part of the actual query.. logically, it's the "last part" of a complete plan, where the actual query result is passed to a cursor operation to sort data as desired..

regards

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If you do not use an ORDER BY clause, SQL Server will produce the data in whatever order it deems efficient.

At times, that may be the order in which the data has been put in the table -but that is just a temporal fluke. There is no guarantee that you will get the data in the same order the next time you query.

To control the presentation, you MUST use an ORDER BY statement.

Here are some other ideas and help about what is often referred to as 'paging' queries:

Paging Queries
www.aspfaq.com/2120

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Thanks very much.

Regards,

Tim