A SQL Server clustered table and an Oracle index only table are essentially the same thing, a table that instead of being heap organised, is stored in sorted order. In the case of Oracle a B*Tree is used and a doubly linked list for SQL Server. But here is the interesting bit, in Oracle due to the expense of secondary index lookups, the use of index organised tables is the excpetion rather than the rule, however if you refer to this presentation from Kimberley Tripp, in SQL Server the use of clustered indexes is encouraged a lot more than their counterparts in Oracle. I can only assume that this is because SQL Server does not have an equivalent to Oracle's table lookup by rowid. In short this took me a bit by surprise.
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