Week 7 notes completed

CM3010 Databases and Advanced Data Techniques/Week 7/Week 7 Notes.md

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+# Using Relational Databases
+
+**SELECT FROM WHERE**
+```SQL
+SELECT *
+FROM Planets
+WHERE diameter > 5;
+```
+
+**Aproximate matching**
+
+```SQL
+SELECT *
+FROM Planets
+WHERE name LIKE '%er';
+```
+where '%er' is a wildcard, it's case insensite, it could be '%ER'
+
+**UPDATE**
+
+```SQL
+UPDATE *
+SET name = 'Mars'
+WHERE anem = 'Mers';
+```
+
+**INSERT**
+
+```SQL
+INSERT INTO Planets (name, diameter)
+VALUES
+    ('Gethen', 9483),
+    ('Athshe', 8210)
+```
+```SQL
+INSERT INTO Planets (name)
+SELECT DISTINCT name
+    FROM Moons;
+```
+Here we have a subquery and we insert the result of this query into the Planets table.
+
+**DELETE**
+
+```SQL
+DELETE FROM Planets
+WHERE diameter < 2500;
+```
+
+**DROP**
+```SQL
+DROP TABLE Planets;
+```
+
+**TRUNCATE**
+```SQL
+TRUNCATE TABLE Planets;
+```
+Removes all entries but leaves the structure.
+
+**CREATE**
+```SQL
+CREATE DATABASE Planets;
+CREATE TABLE Planets (
+    PlanetName CHAR(8),
+    dayLength INT,
+    YearLength INT,
+    PRIMARY KEY (PlanetName)
+);
+```
+
+**ALTER**
+```SQL
+ALTER TABLE Planets
+ADD COLUMN
+    Diameter INT;
+```
+
+## Data exchange
+```SQL
+SELECT *
+FROM Planets
+INTO OUTPUTFILE 'Planets.txt';
+```
+
+```SQL
+LOAD DATA INFILE 'Planets.txt'
+    INTO TABLE Planets;
+```
+
+## Agregate functions
+
+![Diagram](Files/Image1.png)
+We identify who they are for and we group them together
+
+![Diagram](Files/Image2.png)
+
+![Diagram](Files/Image3.png)
+
+We then summarize the information by adding up the price.
+
+![Diagram](Files/Image4.png)
+
+This translates to SQL as:
+
+```SQL
+SELECT *
+    FROM Shopping
+    WHERE
+    BoughtFor = 'Mum';
+```
+
+```SQL
+<SOMETHING>
+    FROM Shopping
+    GROUP BY BoughtFor;
+```
+```SQL
+SELECT BoughtFor,
+    SUM(Price)
+    FROM Shopping
+    GROUP BY BoughtFor;
+```
+This gives us the sum of groups
+
+We also have
+* SUM
+* AVG
+* STD (deviation)
+* VARIANCE
+* MAX (Also works on other data types such as dates, most recent)
+* MIN (least recent or oldest)
+* COUNT
+* COUNT(DISTINCT)
+* GROUP_CONCAT (for strings)
+
+```SQL
+SELECT Gender, COUNT(*) FROM Locations JOIN Actors ON Actor1 = ENName
+GROUP BY Gender;
+```
+```SQL
+SELECT Gender, COUNT(*) FROM Locations JOIN Actors ON Actor2 = ENName
+GROUP BY Gender;
+```
+```SQL
+SELECT Gender, COUNT(*) FROM Locations JOIN Actors ON Actor3 = ENName
+GROUP BY Gender;
+```
+```SQL
+SELECT Actor1, COUNT(*) AS Appearances FROM Locations GROUP BY Actor1 ORDER BY Appearances DESC LIMIT 20;
+```
+(ASC/DESC)
+
+In the Lab
+```SQL
+LOAD DATA
+    INFILE '/home/coder/project/SF_film_locations.csv'
+    REPLACE
+    INTO TABLE Locations
+    FIELDS
+        TERMINATED BY ','
+        OPTIONALLY ENCLOSED BY '"'
+        ESCAPED BY '"'
+    IGNORE 1 ROWS;
+```
+```SQL
+LOAD DATA
+    INFILE '/home/coder/project/wikidata-film-actors.csv'
+    REPLACE
+    INTO TABLE Locations
+    FIELDS
+        TERMINATED BY ','
+        OPTIONALLY ENCLOSED BY '"'
+        ESCAPED BY '"'
+    IGNORE 1 ROWS;
+```
+```SQL
+LOAD DATA
+    INFILE '/home/coder/project/wikidata-film-composers.csv'
+    REPLACE
+    INTO TABLE Locations
+    FIELDS
+        TERMINATED BY ','
+        OPTIONALLY ENCLOSED BY '"'
+        ESCAPED BY '"'
+    IGNORE 1 ROWS;
+```
+
+Age of Actor1
+```SQL
+SELECT DISTINCT Actor1, Year, DOB, FLOOR(DATEDIFF(MakeDate(Year, 1), DOB)/365) AS Age, Title AS Movie FROM Locations JOIN Actors ON Actor1 = ENName LIMIT 20;
+```
+
+Update the age of Charles Chaplin
+``` SQL
+UPDATE Actors SET DOB = '1889-04-16' WHERE ENName = 'Charles Chaplin';
+```
+
+## Database libraries
+* Create a (persistent) connection
+* Send commands
+* Receive (and structure) response
+
+## Create a (persistent) connection
+`conn <- newCnnection(host, username, password, database)`
+`conn.connect()`
+
+Or both steps in one
+
+`conn <- connect(host, username, password, database)`
+
+## Sending commands
+`resource <- conn.execute(query)`
+`resource.fetchData()`
+
+Or
+
+`result <- conn.query(query)`
+
+## Receive response
+The result will usually be iterable.
+
+Each row may be an object or an array.
+
+## Using PHP SQL libraries
+
+```PHP
+$db = new mysqli(host, user, pwd, db);
+```
+
+```PHP
+$result = $db->query("SELECT * FROM Planets");
+```
+Returns a mysqli_result object
+
+We can iterate through this response
+```PHP
+foreach ($result as $moon) {
+    echo $moon['radius'];
+}
+```
+or treat it as a 2D array
+```PHP
+$moons = $result->fetch_all();
+echo $moons[5][2];
+```
+or provide an option to use keys
+```PHP
+$moons = $result->fetch_all(MYSQL_ASSOC);
+echo $moons[5]['radius'];
+```