that's a wrap

11-7-18.sql

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+-- aggregate functions
+
+-- COUNT()
+
+-- we're using the ZAGI database (and associated example commands)
+
+-- number of rows (* can also be replaced with a primary key?)
+COUNT(*)
+
+-- number of entries
+COUNT(field)
+
+-- ZAGI 13
+COUNT (*)
+FROM product;
+
+-- returns number or rows
+
+-- 15
+
+-- returns count, avg, min, max
+
+-- 16
+
+-- for each vendor id, get total number of product, and the average product price, sorted by vendor id.
+
+-- returns vid, count, avg
+
+
+-- GROUP BY xxxxx
+-- must have xxxx in the select statement, otherwise we can get errors
+
+-- 17 is highly un-recommended. it doesn't indicate what the data is sorted by (context)
+
+-- 18
+
+-- returns vid and count of products over 100$
+
+-- 19
+
+-- average product prices by category
+
+-- 20
+
+-- retunrs productid and the number of items sold
+
+-- SUM()
+
+-- shows a sum of the items
+
+-- 21
+
+-- shows number of transactions for each one, grouped by product
+
+-- HAVING
+-- similar to WHERE, used for a grouping feature, generally found after a GROUP BY statement
+
+-- enhanced query based on 28
+
+SELECT productid, productname, productprice, (
+  SELECT AVG(productprice) FROM product
+) AS avg_price
+FROM product
+WHERE productprice < (
+  SELECT AVG (productprice)
+  FROM product
+);
+
+-- notice that we can't just do WHERE productprice < avg_price. That's a bit derp. Some SQL db's can handle that, but ours (mySQL?) appears that it cannot
+-- switching to SQL zoo after q30
+
+
+
+
+
+-- dataset is now world(name, continent, area, population, gdp)
+
+-- q2 show the countries with a per capita GDP greater than the UK
+SELECT name
+FROM world
+WHERE continent = 'Europe'
+AND gdp/population > (
+  SELECT gdp/population AS percapitagdp
+  FROM world
+  WHERE name = 'United Kingdom'
+);
+
+-- he did this first:
+SELECT gdp/population AS percapitagdp
+FROM world
+WHERE name = 'United Kingdom';
+
+-- q3 List the names and continent of countries in the continents containng either Argentena or Australia, and order by country
+SELECT name, continent
+FROM world
+WHERE continent IN (
+  SELECT continent
+  FROM world
+  WHERE name IN ('Argentena', 'Australia')
+)
+ORDER BY name;
+
+-- he did this first
+SELECT continent
+FROM world
+WHERE name IN ('Argentena', 'Australia');
+
+-- q4 Which country has a population that is more than Canada and less than poland? Show the name and the population.
+SELECT name, country
+FROM world
+WHERE population > (
+  SELECT population
+  FROM world
+  WHERE name = 'Canada'
+)
+AND population < (
+  SELECT population
+  FROM world
+  WHERE name = 'Poland'
+);
+
+-- I came up with these first. He started with the external query first
+SELECT population
+FROM world
+WHERE name = 'Canada';
+
+SELECT population
+FROM world
+WHERE name = 'Poland';
+
+-- show the inner query results for more context as to how the numbers compares
+SELECT name, country, (
+  SELECT population
+  FROM world
+  WHERE name = 'Canada'
+) as popCanada, (
+  SELECT population
+  FROM world
+  WHERE name = 'Poland'
+) as popPoland
+FROM world
+WHERE population > (
+  SELECT population
+  FROM world
+  WHERE name = 'Canada'
+)
+AND population < (
+  SELECT population
+  FROM world
+  WHERE name = 'Poland'
+);
+
+-- q5 Germany, population 80 million has the largest population of the countries in Europe.
+-- Show the name and population of each country in Europe
+-- Show the population as a percentage of the population of Germany
+
+-- I made this first
+SELECT population
+FROM world
+WHERE name = 'Germany';
+
+-- first round
+SELECT name, population/(
+  SELECT population
+  FROM world
+  WHERE name = 'Germany'
+) AS popPctgOfGermany
+FROM world
+WHERE continent = 'Europe';
+
+-- second round - add rounding statement and multiply by 100 to get percentage
+SELECT name, ROUND (
+  100 * population/(
+    SELECT population
+    FROM world
+    WHERE name = 'Germany'
+  ), 0 -- number of decimal places
+) AS popPctgOfGermany
+FROM world
+WHERE continent = 'Europe';
+
+-- third round - add percent symbol with || '%'
+SELECT name, ROUND (
+  100 * population/(
+    SELECT population
+    FROM world
+    WHERE name = 'Germany'
+  ), 0 -- number of decimal places
+) || '%' AS popPctgOfGermany
+FROM world
+WHERE continent = 'Europe';
+
+-- q6 Which countries have a GDP greater than every contry in Europe (name only, some countries may have NULL GDP values)
+-- we need to find the greatest GDP in Europe as well
+SELECT name
+FROM world
+WHERE gdp > (
+  SELECT MAX(gdp)
+  FROM world
+  WHERE continent = 'Europe'
+)
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+--