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I understand that prior to SQL Server 2005, you could "trick" SQL Server to allow use of an order by in a view definition, by also include TOP 100 PERCENT in the SELECT clause. But I have seen other code which I have inherited which uses SELECT TOP 100 PERCENT ... within dynamic SQL statements (used in ADO in ASP.NET apps, etc). Is there any reason for this? Isn't the result the same as not including the TOP 100 PERCENT?
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TOP (100) PERCENT is completely meaningless in recent versions of SQL Server, and it (along with the corresponding ORDER BY, in the case of a view definition or derived table) is ignored by the query processor. You're correct that once upon a time, it could be used as a trick, but even then it wasn't reliable.
So if we see TOP (100) PERCENT in code, we suspect that the developer has attempted to create an ordered view and we check if that's important before going any further. Chances are that the query that uses that view (or the client application) need to be modified instead.
The SELECT TOP clause is used to specify the number of records to return. The SELECT TOP clause is useful on large tables with thousands of records. Returning a large number of records can impact performance.
Example - Using TOP PERCENT keyword For example: SELECT TOP(10) PERCENT employee_id, last_name, first_name FROM employees WHERE last_name = 'Anderson' ORDER BY employee_id; This SQL Server SELECT TOP example would select the first 10% of the records from the full result set.
It was used for "intermediate materialization (Google search)"
Good article: Adam Machanic: Exploring the secrets of intermediate materialization
He even raised an MS Connect so it can be done in a cleaner fashion
My view is "not inherently bad", but don't use it unless 100% sure. The problem is, it works only at the time you do it and probably not later (patch level, schema, index, row counts etc)...
This may fail because you don't know in which order things are evaluated
SELECT foo From MyTable WHERE ISNUMERIC (foo) = 1 AND CAST(foo AS int) > 100 And this may also fail because
SELECT foo FROM (SELECT foo From MyTable WHERE ISNUMERIC (foo) = 1) bar WHERE CAST(foo AS int) > 100 However, this did not in SQL Server 2000. The inner query is evaluated and spooled:
SELECT foo FROM (SELECT TOP 100 PERCENT foo From MyTable WHERE ISNUMERIC (foo) = 1 ORDER BY foo) bar WHERE CAST(foo AS int) > 100 Note, this still works in SQL Server 2005
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