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
...allow use of an ORDER BY in a view definition.
That's not a good idea. A view should never have an ORDER BY defined.
An ORDER BY has an impact on performance - using it a view means that the ORDER BY will turn up in the explain plan. If you have a query where the view is joined to anything in the immediate query, or referenced in an inline view (CTE/subquery factoring) - the ORDER BY is always run prior to the final ORDER BY (assuming it was defined). There's no benefit to ordering rows that aren't the final result set when the query isn't using TOP (or LIMIT for MySQL/Postgres).
Consider:
CREATE VIEW my_view AS
SELECT i.item_id,
i.item_description,
it.item_type_description
FROM ITEMS i
JOIN ITEM_TYPES it ON it.item_type_id = i.item_type_id
ORDER BY i.item_description
...
SELECT t.item_id,
t.item_description,
t.item_type_description
FROM my_view t
ORDER BY t.item_type_description
...is the equivalent to using:
SELECT t.item_id,
t.item_description,
t.item_type_description
FROM (SELECT i.item_id,
i.item_description,
it.item_type_description
FROM ITEMS i
JOIN ITEM_TYPES it ON it.item_type_id = i.item_type_id
ORDER BY i.item_description) t
ORDER BY t.item_type_description
This is bad because:
ORDER BY item_type_description, item_description
No reason but indifference, I'd guess.
Such query strings are usually generated by a graphical query tool. The user joins a few tables, adds a filter, a sort order, and tests the results. Since the user may want to save the query as a view, the tool adds a TOP 100 PERCENT. In this case, though, the user copies the SQL into his code, parameterized the WHERE clause, and hides everything in a data access layer. Out of mind, out of sight.
I have seen other code which I have inherited which uses SELECT TOP 100 PERCENT
The reason for this is simple: Enterprise Manager used to try to be helpful and format your code to include this for you. There was no point ever trying to remove it as it didn't really hurt anything and the next time you went to change it EM would insert it again.
If there is no ORDER BY
clause, then TOP 100 PERCENT
is redundant. (As you mention, this was the 'trick' with views)
[Hopefully the optimizer will optimize this away.]