Difference between revisions of "2015 UK General Election using SQL Server"

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(Who won the election?)
(Who won the election?)
 
Line 67: Line 67:
 
==Who won the election?==
 
==Who won the election?==
 
The important question is which party got the most seats. Which party leader should the queen invite to form a government?
 
The important question is which party got the most seats. Which party leader should the queen invite to form a government?
We can use the [[rank()]] function for this but we prefer to use a slower, simpler solution:
+
We can use the [[RANK]] function for this but we prefer to use a slower, simpler solution:
  
 
First calculate the max votes per constituency:
 
First calculate the max votes per constituency:

Latest revision as of 08:33, 5 July 2017

This tutorial assumes you have access to powershell and sqlcmd or Microsoft SQL Server Management Studio

Get to the powershell prompt and download the csv

Invoke-WebRequest http://researchbriefings.files.parliament.uk/documents/CBP-7979/hocl-ge2017-results-full.csv -OutFile ge2017.csv

Go into sqlcmd or SSMS and create a table for the results

Here you create a single flat table that can store all of the unnormalised data.

The first line of the CSV file contains the column headings (ons_id,ons_region_id,constituency_name,county_name,region_name,country_name,constituency_type,party_name,party_abbreviation,firstname,surname,gender,sitting_mp,former_mp,votes,share,change). We create a table with a column for each of these:

sqlcmd -S .\sqlexpress -E

We do not know the size of each column yet, too small and the import statement will give errors or warnings. It is best to be generous - memory is cheap.

The create table statement could be:

CREATE TABLE ge(
  ons_id VARCHAR(10),
  ons_region_id VARCHAR(10),
  constituency_name VARCHAR(50),
  county_name VARCHAR(50),
  region_name VARCHAR(50),
  country_name VARCHAR(50),
  constituency_type VARCHAR(10),
  party_name VARCHAR(50),
  party_abbreviation VARCHAR(50),
  firstname VARCHAR(50),
  surname VARCHAR(50),
  gender VARCHAR(6),
  sitting_mp VARCHAR(3),
  former_mp VARCHAR(3),
  votes INT,
  share FLOAT,
  change VARCHAR(20),
  PRIMARY KEY(ons_id,firstname,surname)
)

Attempt import the csv file into your flat table

You can import the data using this line (from SQLCMD or SQL Server Management Studio)

BULK INSERT ge FROM 'C:\db\ge2017.csv' WITH (FIELDTERMINATOR=',', ROWTERMINATOR='\n', FIRSTROW=2)
GO
  • Each line is ended with carriage return \n
  • The first row contains column headings not data so we start at row 2

You will most likely get error messages like this:

Msg 4863, Level 16, State 1, Server ME1C039-130368\SQLEXPRESS, Line 3
Bulk load data conversion error (truncation) for row 105, column 13 (sitting_mp).
Msg 4863, Level 16, State 1, Server ME1C039-130368\SQLEXPRESS, Line 3
Bulk load data conversion error (truncation) for row 106, column 12 (gender).
Msg 4863, Level 16, State 1, Server ME1C039-130368\SQLEXPRESS, Line 3
Bulk load data conversion error (truncation) for row 107, column 13 (sitting_mp).
...

Unfortunately BULK INSERT cannot deal with the CSV format so we need to pre-process the file. Some solutions:

  • Use Excel - you can load CSV and save as TXT
  • Use regular expressions in powershell: convert CSV to TXT
  • Use python
  • Find a converter online

With the conversion complete you can import the data - you will have too use the full path name and you may have permissions problems

BULK INSERT ge FROM 'c:\path\ge2017.txt' WITH (FIRSTROW=2)

You may get a few errors - it is probably easiest to fix these "by hand" using Excel or a text editor. The BULK INSERT command should show you the line numbers. Check that you have the correct number of rows - there should be 3304 data rows.

SELECT COUNT(*) FROM ge

Run some queries

Now let's look at some data. How many female candidates were there?

select count(1) from ge where gender='female';

Who stood in Edinburgh South?

select surname,votes from ge where constituency_name='Edinburgh South';

Who won the election?

The important question is which party got the most seats. Which party leader should the queen invite to form a government? We can use the RANK function for this but we prefer to use a slower, simpler solution:

First calculate the max votes per constituency:

SELECT ons_id,MAX(votes) AS mv
  FROM ge
GROUP BY ons_id

Now JOIN that to the original table to find the party that won each seat:

SELECT ge.ons_id, ge.party_name
  FROM ge JOIN
       (SELECT ons_id,MAX(votes) AS mv
          FROM ge
        GROUP BY ons_id) AS ms ON ge.ons_id=ms.ons_id AND ge.votes=ms.mv

We can now count the seats by party:

SELECT party_name,COUNT(1) TotSeat
  FROM (
    SELECT ge.ons_id, ge.party_name
      FROM ge JOIN
          (SELECT ons_id,MAX(votes) AS mv
             FROM ge
           GROUP BY ons_id) AS ms ON ge.ons_id=ms.ons_id AND ge.votes=ms.mv
       ) AS mp
GROUP BY party_name

You can now move to the next stage: 2015 UK General Election Normalising Data