Date: Mon, 1 Jun 2015 19:11:15 +0000 (UTC)
From: Kevin Grittner <kgrittn@ymail.com>
Reply-To: Kevin Grittner <kgrittn@ymail.com>
To: "er.tejaspatel88@gmail.com" <er.tejaspatel88@gmail.com>,
 "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Message-ID: <1217472852.2845919.1433185875147.JavaMail.yahoo@mail.yahoo.com>
In-Reply-To: <1431941415888-5849705.post@n5.nabble.com>
References: <1431941415888-5849705.post@n5.nabble.com>
Subject: Re: Fastest way / best practice to calculate "next
 birthdays"
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"er.tejaspatel88@gmail.com" <er.tejaspatel88@gmail.com> wrote:

> If I have to find upcoming birthdays in current week and the
> current week fall into different months - how would you handle
> that?

If you don't need to cross from December into January, I find the
easiest is:

SELECT * FROM person
  WHERE (EXTRACT(MONTH FROM dob), EXTRACT(DAY FROM dob))
          BETWEEN (6, 28) AND (7, 4);

That is logicically the same as:

SELECT * FROM person
  WHERE (EXTRACT(MONTH FROM dob) >= 6
    AND (EXTRACT(MONTH FROM dob) > 6
     OR (EXTRACT(DAY FROM dob) >= 28)))
    AND (EXTRACT(MONTH FROM dob) <= 7
    AND (EXTRACT(MONTH FROM dob) < 7
     OR (EXTRACT(DAY FROM dob) <= 4)));

That's the generalized case; with the months adjacent, this simpler
form is also equivalent:

SELECT * FROM person
  WHERE (EXTRACT(MONTH FROM dob) = 6
    AND EXTRACT(DAY FROM dob) >= 28)
    OR (EXTRACT(MONTH FROM dob) = 7
    AND EXTRACT(DAY FROM dob) <= 4);

The first query I showed is faster than either of the alternatives,
especially if there is an index on dob.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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