9-_window_function.sql

--1. Show the lastName, party and votes for the constituency 'S14000024' in 2017.

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


--2. 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) FROM ge
  WHERE constituency = 'S14000024' AND yr = 2017
  ORDER BY party;


--3. 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. Include yr, party, votes and ranking (the party with the most votes is 1).

SELECT yr, party, votes, 
       RANK() OVER(PARTITION BY yr ORDER BY votes DESC) 
FROM ge
  WHERE constituency = 'S14000021';


--4. 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,
       RANK() OVER(PARTITION BY constituency 
                   ORDER BY votes DESC) AS rank
FROM ge
  WHERE constituency BETWEEN 'S14000021' AND 'S14000026'
  AND yr = 2017
  ORDER BY rank, constituency;


--5. You can use SELECT within SELECT to pick out only the winners in Edinburgh.

--Solution 1:
SELECT constituency, party FROM
  (SELECT constituency, 
          party, 
          RANK() OVER(PARTITION BY constituency 
                      ORDER BY votes DESC) AS posn
   FROM ge
    WHERE yr = 2017 
    AND constituency BETWEEN 'S14000021' AND 
                             'S14000026') AS x
  WHERE posn = 1;


--Solution 2:
SELECT constituency, party FROM ge AS x
  WHERE yr = 2017 
  AND constituency BETWEEN 'S14000021' AND 'S14000026'
  AND votes = 
    (SELECT MAX(votes) FROM ge AS y
      WHERE y.constituency = x.constituency
      AND y.yr = x.yr);


--6. You can use COUNT and GROUP BY to see how each party did in Scotland. Scottish constituencies start with 'S'
--Show how many seats for each party in Scotland in 2017.

--Solution 1:
SELECT party, COUNT(*) FROM
  (SELECT party, 
          RANK() OVER(PARTITION BY constituency
                      ORDER BY votes DESC) AS posn 
   FROM ge
    WHERE constituency LIKE 'S%' AND yr = 2017) AS x
  WHERE posn = 1
  GROUP BY party;

--Solution 2:
SELECT party, COUNT(*) FROM ge AS x
  WHERE constituency LIKE 'S%'
  AND yr = 2017
  AND votes = (SELECT MAX(votes) FROM ge AS y
                WHERE y.constituency = x.constituency
                AND y.yr = x.yr)
  GROUP BY party;