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

PostGres - Advanced

Lesson Objectives - important

1. Linking Tables
2. Alias
3. Indexes
4. Default Values
5. Constraints
6. 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 -> SQL

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. Primary Key
4. use \d table_name to view indexes

Default Values

CREATE TABLE people (id SERIAL, name VARCHAR(16), age INT DEAFULT 0);
\d people

INSERT INTO people (name) VALUES ('matt');
SELECT * FROM people;

Constraints

1. NOT NULL
2. Unique
3. Foreign Keys

CREATE TABLE companies(
	id SERIAL,
	name VARCHAR(16)  NOT NULL,
	city VARCHAR(16)
);

INSERT INTO companies ( city ) VALUES ('Palo Alto');

CREATE TABLE people(
	id INT,
	name VARCHAR(16),
	email VARCHAR(32) UNIQUE,
	company_id INT REFERENCES companies(id)
);

\d people

INSERT INTO people (name, email, company_id) VALUES ('bob', 'bob@bob.com', 999) -- bad company_id
INSERT INTO people (name, email, company_id) VALUES ('bob', 'bob@bob.com', 1) -- not unique email

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';

\dv

SELECT * FROM new_yorkers

Functions

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

\df

SELECT add_numbers(2,4);

Stored Procedures

CREATE PROCEDURE add_person(new_name VARCHAR(16))
LANGUAGE plpgsql
AS $$
BEGIN
	INSERT INTO people (name) VALUES (new_name);
END
$$;

\df

call add_person('matt');

Triggers

CREATE TABLE backup_people (id INT, name VARCHAR(16), age INT);

CREATE FUNCTION moveDeleted() RETURNS trigger AS $$
	BEGIN
		INSERT INTO backup_people VALUES (OLD.id, OLD.name, OLD.age);
	RETURN OLD;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER archive_person
	BEFORE DELETE on people
	FOR EACH ROW
	EXECUTE PROCEDURE moveDeleted();

\df

DELETE FROM people WHERE id = 1;

Transactions

BEGIN;

INSERT INTO people (name) VALUES ('matt');

SELECT * FROM people;

-- start a different session and run SELECT * FROM people;
-- Switch back to original session

COMMIT;

-- in other session run SELECT * FROM people;

OR

BEGIN;

INSERT INTO people (name) VALUES ('matt');

SELECT * FROM people;

asdfasdfasdfasdfasdfasdf;

ROLLBACK;

SELECT * FROM people;

Locks

BEGIN;
LOCK TABLE people IN ROW EXCLUSIVE MODE;
SELECT * FROM people WHERE id = 12 FOR UPDATE;

-- start a new session and run UPDATE people SET name = 'Matt' WHERE id = 12;
-- switch back to original session

UPDATE people SET age = 43 WHERE id = 12;
SELECT * FROM people;
END;

Privileges

Denormalization

id	name	age	company_id	company_name	company_address
1	matt	43	1	google	SF

Excel -> CSV -> SQL

• Create sheet
• File -> Download -> .csv
• COPY people (name, age, ancestry, city) FROM '/Users/matthuntington/Downloads/people.csv' DELIMITER ',' CSV;

SQL Injection

• input with value Huntington'; DROP TABLE people;