Re: PostgreSQL - 'SKYLINE OF' clause added! - Mailing list pgsql-hackers

Skyline operator finds points which are not dominated by other data points. A point dominates another point if it is as good or better in all dimensions and better in at least one dimension.

For specifying the Skyline queries, we extend SQL SELECT statement by an optional SKYLINE OF clause as given below:           

SELECT ... FROM ... WHERE...

GROUP BY ... HAVING...

SKYLINE OF [DISTINCT] d1 [MIN | MAX | DIFF],  .., dm [MIN | MAX | DIFF]

ORDER BY...

 
Where, d1, d2 ,…, dm denote the dimensions of the Skyline, and MIN, MAX, DIFF specify whether the value in that dimension should be minimized, maximized, or simply be different. When DIFF is specified, two tuples are compared only if the value of the attribute on which DIFF is applied is different.

When DISTINCT clause is specified and if there are two or more tuples with the same values of skyline attributes, then only one of them is retained in the skyline set. Otherwise, all of them are retained.

Let's consider the above example of purchasing books with high rating and low price.

Table1. Sample of book database

Now, in order to get books with high rating and low price, you simply can issue the following query:

SELECT *

FROM Books

SKYLINE OF rating MAX, price MIN;

The Skyline set returned will be:

Table2. Skyline set

From this set, you can now make your choice of books, by weighing your personal preferences for price and rating of the books.

For more information, you can refer to:
S. Borzsonyi, D. Kossmann, and K. Stocker. The skyline operator. In ICDE, pages 421.430, 2001

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Thanks.