Difference between revisions of "Scottish Parliament"

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(fix syntax error in answer)
 
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<source lang='sql' class='ans'>
 
<source lang='sql' class='ans'>
 
SELECT name, leader FROM party
 
SELECT name, leader FROM party
   WHERE leader IS NOT NUL
+
   WHERE leader IS NOT NULL
 
</source>
 
</source>
 
</div>
 
</div>

Latest revision as of 12:26, 31 May 2014

Scottish Parliament

The data includes all Members of the Scottish Parliament (MSPs) in 1999. Most MSPs belong to a political party. Some parties have a leader who is an MSP. There are two tables:

msp
Name Party Constituency
Adam MSP, BrianSNPNorth East Scotland
Aitken MSP, BillConGlasgow
Alexander MSP, Ms WendyLabPaisley North
... Total number of records: 129
party
Code Name Leader
ConConservativeMcLetchie MSP, David
GreenGreen
LabLabourDewar MSP, Rt Hon Donald
... Total number of records: 9

Selecting NULL values

Dealing wit NULL

One MSP was kicked out of the Labour party and has no party. Find him.

You might think that the phrase dept=NULL would work here. It doesn't. This is because NULL "propogates". Any normal expression that includes NULL is itself NULL, thus the value of the expressions 2+NULL and party || NULL and NULL=NULL for example are all NULL.

The NULL value does not cause a type error, however it does infect everything it touches with NULL-ness. We call this element the bottom value for the algebra - but we don't snigger because we are grown-ups. Bottom Type.

 
SELECT name FROM msp WHERE party IS NULL

Obtain a list of all parties and leaders.

 
SELECT name, leader FROM party

Give the party and the leader for the parties which have leaders.

 
SELECT name, leader FROM party
  WHERE leader IS NOT NULL

Obtain a list of all parties which have at least one MSP.

 
SELECT DISTINCT party.name FROM msp, party
  WHERE party=code

Outer joins

Obtain a list of all MSPs by name, give the name of the MSP and the name of the party where available. Be sure that Canavan MSP, Dennis is in the list. Use ORDER BY msp.name to sort your output by MSP.

 
SELECT msp.name, party.name
  FROM msp LEFT JOIN party ON party=code
  ORDER BY msp.name


Obtain a list of parties which have MSPs, include the number of MSPs.

 
SELECT party.name, COUNT(msp.name)
  FROM msp, party
  WHERE msp.party=party.code
  GROUP BY party.name

A list of parties with the number of MSPs; include parties with no MSPs.

 
SELECT party.name, COUNT(msp.name)
  FROM party 
  LEFT JOIN msp ON party.code=msp.party
  GROUP BY party.name

Self joins are the topic for the next tutorial

Note

Sadly Donald Dewar died in 2000. An able and popular leader of the Labour Party in Scotland.

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