python-sql-lessons/SQL/lessons/sql_3.md

PostGres - Advanced

Lesson Objectives - important

1. Linking Tables
2. Alias
3. Indexes
4. Constraints
5. Distinct

Lesson Objectives - good to know about

1. EER Diagrams
2. Unions
3. Truncate
4. Views
5. Functions
6. Stored Procedures
7. Triggers
8. Transactions
9. Locks
10. Privileges
11. Denormalization
12. Excel -> CSV -> MySQL

Important

Linking Tables

1. Some Nice Visuals
2. One to Many/Many to One Relationships
   • customer has many orders
3. One to One Relationships
   • each user has one address
   • only one person at that address
4. Many to Many Relationships
   • actors and movies
5. Self Referncing Relationships
   • customer referral

Alias

SELECT t1.column1 as col1, t2.column2 as col2
FROM table1 as t1
INNER JOIN table2 as t2
ON t1.common_filed = t2.common_field;

Indexes

1. CREATE INDEX index_name ON table_name (column_name);
2. CREATE INDEX index_name ON table_name (column1_name, column2_name);
3. use \d table_name to view indexes
4. Primary Key

Constraints

1. NOT NULL
2. Unique
3. Foreign Keys

CREATE TABLE companies(
  id          SERIAL       PRIMARY KEY,
  name        VARCHAR(16)  NOT NULL UNIQUE,
  city        VARCHAR(16)
);
INSERT INTO companies ( city ) VALUES ('Palo Alto');
CREATE TABLE people(
  id          INT          PRIMARY KEY,
  name        VARCHAR(16)  NOT NULL,
  email       VARCHAR(32)  NOT NULL UNIQUE,
  company_id  INT          REFERENCES companies(id)
);
INSERT INTO people (name, email, company_id) VALUES ('bob', 'bob@bob.com', 999)

Distinct

SELECT DISTINCT city FROM people;

Good to Know About

EER Diagrams

Unions

SELECT name FROM people UNION SELECT name FROM companies; -- show distinct values
SELECT name FROM people UNION ALL SELECT name FROM companies; -- show duplicates

Truncate

TRUNCATE TABLE people; -- delete all data, but don't delete table itself

Views

CREATE VIEW new_yorkers AS SELECT * FROM people WHERE city = 'NYC';
SELECT * FROM new_yorkers

Functions

CREATE FUNCTION add_numbers(a integer, b integer)
RETURNS integer AS $$
BEGIN
	RETURN a + b;
END; $$
LANGUAGE plpgsql;

SELECT add_numbers(2,4);

Stored Procedures

Triggers

Transactions

Locks

Privileges

Denormalization

Excel -> CSV -> MySQL

SQL Injection