Difference between revisions of "Window functions"

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   AND yr  = 2017
 
   AND yr  = 2017
 
ORDER BY posn,constituency
 
ORDER BY posn,constituency
 +
</source>
 +
</div>
 +
 +
==Winners Only==
 +
<div class='qu'>
 +
You can use [[Nested SELECT]] to pick out only the winners in Edinburgh.
 +
<div class='imper'>Show the parties that one for each Edinburgh constituency in 2017.</div>
 +
<source lang='sql' class='def'>
 +
SELECT constituency,party, votes
 +
  FROM ge
 +
WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
 +
  AND yr  = 2017
 +
ORDER BY constituency,votes DESC
 +
</source>
 +
<source lang='sql' class='ans'>
 +
SELECT constituency, party
 +
  FROM (
 +
    SELECT constituency,party,
 +
      RANK() OVER (PARTITION BY constituency ORDER BY votes DESC)
 +
        AS posn
 +
      FROM ge
 +
    WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
 +
      AND yr  = 2017
 +
  ) AS ed
 +
WHERE posn = 1
 
</source>
 
</source>
 
</div>
 
</div>

Revision as of 13:25, 23 November 2019

General Elections were held in the UK in 2015 and 2017. Every citizen votes in a constituency. The candidate who gains the most votes becomes MP for that constituency.

Warming up

Show the lastName, party and votes for the constituency 'S14000024' in 2019.

SELECT lastName, party, votes
  FROM ge
 WHERE constituency = 'E14000539' AND yr = 2017
ORDER BY votes DESC
SELECT lastName, party, votes
  FROM ge
 WHERE constituency = 'S14000024' AND yr = 2017
ORDER BY votes DESC

Who won?

You can use the RANK function to see the order of the candidates. If you RANK using (ORDER BY votes DESC) then the candidate with the most votes has rank 1.

Show the party and RANK for constituency S14000024 in 2017. List the output by party
SELECT party, votes,
       RANK() OVER (ORDER BY votes DESC) as posn
  FROM ge
 WHERE constituency = 'E14000539' AND yr = 2017
ORDER BY votes
SELECT party, votes,
       RANK() OVER (ORDER BY votes DESC) as posn
  FROM ge
 WHERE constituency = 'S14000024' AND yr = 2017
ORDER BY party

PARTITION BY

The 2015 election is a different PARTITION to the 2017 election. We only care about the order of votes for each year.

Use PARTITION to show the ranking of each party in S14000021 in each year.
SELECT yr,party, votes,
      RANK() OVER (PARTITION BY yr ORDER BY votes DESC) as posn
  FROM ge
 WHERE constituency = 'S14000021'
ORDER BY party,yr
SELECT yr,party, votes,
      RANK() OVER (PARTITION BY yr ORDER BY votes DESC) as posn
  FROM ge
 WHERE constituency = 'S14000021'
ORDER BY party,yr

Edinburgh Constituency

Edinburgh constituencies are numbered S14000021 to S14000026.

Use PARTITION BY constituency to show the ranking of each party in Edinburgh in 2017. Order your results so the winners are shown first, then ordered by constituency.
SELECT constituency,party, votes
  FROM ge
 WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
   AND yr  = 2017
ORDER BY constituency,votes DESC
SELECT constituency,party, votes,
  RANK() OVER (PARTITION BY constituency ORDER BY votes DESC)
    AS posn
  FROM ge
 WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
   AND yr  = 2017
ORDER BY posn,constituency

Winners Only

You can use Nested SELECT to pick out only the winners in Edinburgh.

Show the parties that one for each Edinburgh constituency in 2017.
SELECT constituency,party, votes
  FROM ge
 WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
   AND yr  = 2017
ORDER BY constituency,votes DESC
SELECT constituency, party
  FROM (
    SELECT constituency,party,
      RANK() OVER (PARTITION BY constituency ORDER BY votes DESC)
        AS posn
      FROM ge
     WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
       AND yr  = 2017
   ) AS ed
WHERE posn = 1