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DENSE_RANK and KEEP

shacho
shacho asked
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Last Modified: 2014-05-14
I apologize for the newbishness of this question - it's been a long time since I used SQL.

I am picking apart some SQL and trying to understand its logic.  The core of the SQL is essentially this:

SELECT
  PROD_ID
  MAX(PROD_SIZE) KEEP (DENSE_RANK FIRST ORDER BY STORE_ID) AS PROD_SIZE
FROM PRODUCTS
GROUP BY
  PROD_ID

I need to understand in plain English what's happening here.  I can't get my mind around what KEEP does, and how and why DENSE_RANK is here.  Can someone help me work through this?
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