Re: simple SQL question - Mailing list pgsql-sql

From: Dan McFadyen [mailto:danm@cryptocard.com]
Sent: Friday, March 20, 2009 3:51 PM
To: Kevin Duffy
Subject: RE: [SQL] simple SQL question

Hello All:

I would like your input on how I should approach a problem.

Say I have a table of companies and one attribute is the market capitalization of these companies.

I have another table (definition below) and it contains capitalization levels.

For example Micro Cap, Mid Cap, and Large Cap.    However, the table

CAPITALIZATIONLEVEL, only contains the upper cutoff of the levels.

The question is: What is the most efficient way to assign/join the capitalization levels to the companies?

I could create a function that given a market cap in millions would return the matching cap level,

by using a cursor to step through CAPITALIZATIONLEVEL  from lowest to highest.

This function would be declared STABLE.

-or maybe-

a function that RETURNS SETOF and the rows in the set returned would contain both the lower and

upper limits of the cap level.  The lower limit would be calc’ed  by using a cursor to step through

CAPITALIZATIONLEVEL  from lowest to highest.  This function would be declared STABLE.

Which method would execute more efficiently? 

Thanks for considering my issue.

Kevin Duffy

CREATE TABLE capitalizationlevel

(

  capitallevelkey serial NOT NULL,

  caplevelname character(10) NOT NULL,

  caplevelmillions integer NOT NULL,     ß this is the upper limit

  CONSTRAINT pk_capitalizationlevel PRIMARY KEY (capitallevelkey)

)

WITH (OIDS=FALSE);

ALTER TABLE capitalizationlevel OWNER TO postgres;