How TOP query will work in SQL Server?

Hi Experts,
  While running TOP command, what internally happen in SQL Server Engine ? How its fetching TOP 10 rows from Table.
Thanks
Selva

That is the *logical* query processing order, which isn't the same as the *physical* processing order.
As for how SQL Server performs TOP, then as syggested it very much depends on whether there is an ORDER BY or not. Since, TOP is logically processed after ORDER BY, you change the semantics of the TOP operation a lot when you add ORDER BY. But as usual,
we can't say anything about the physcial query order with having an example to talk about. Too many involved factors, like how the rest of the query look like, the schema, what indexes we have, data distribution etc.
Tibor Karaszi, SQL Server MVP |
web | blog

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