Sequence Tables

It is frequently useful to generate sequences of values within SQL Server, perhaps for use as surrogate keys. Using the IDENTITY property on a column is the easiest way to automatically generate such sequences:

CREATE TABLE dbo.SomeTable
(
    row_id integer IDENTITY PRIMARY KEY,
    [data] sql_variant NOT NULL,
);

Sometimes though, the database designer needs a more flexible scheme than is provided by the IDENTITY property. One alternative is to use a Sequence Table.

Ranking Function Optimizer Transformations

In my last post I showed how SQL Server 2005 and later can use a Segment Spool to implement aggregate window functions and the NTILE ranking function.

The query optimizer is also smart enough to recognise that some queries are logically equivalent to a window function, even if they are written using different syntax.