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

# PostGres - Advanced

## Lesson Objectives - important

1. Linking Tables
1. Alias
1. Indexes
1. Default Values
1. Constraints
1. Distinct

## Lesson Objectives - good to know about

1. EER Diagrams
1. Unions
1. Truncate
1. Views
1. Functions
1. Stored Procedures
1. Triggers
1. Transactions
1. Locks
1. Privileges
1. Denormalization
1. Excel -> CSV -> SQL

## Important

### Linking Tables

1. [Some Nice Visuals](http://code.tutsplus.com/articles/sql-for-beginners-part-3-database-relationships--net-8561)
1. One to Many/Many to One Relationships
	- customer has many orders
1. One to One Relationships
	- each user has one address
	- only one person at that address
1. Many to Many Relationships
	- actors and movies
1. Self Referncing Relationships
	- customer referral

### Alias

```sql
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);`
1. `CREATE INDEX index_name ON table_name (column1_name, column2_name);`
1. Primary Key
1. use `\d table_name` to view indexes

### Default Values

```sql
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	
1. Unique
1. Foreign Keys

```sql
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

```sql
SELECT DISTINCT city FROM people;
```

## Good to Know About

### EER Diagrams

![](https://cdn.tutsplus.com/cdn-cgi/image/width=992/net/uploads/legacy/538_sql3/ss_6.png)

### Unions

```sql
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

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

### Views

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

\dv

SELECT * FROM new_yorkers
```

### Functions

```sql
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

```sql
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

```sql
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

```sql
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

```sql
BEGIN;

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

SELECT * FROM people;

asdfasdfasdfasdfasdfasdf;

ROLLBACK;

SELECT * FROM people;
```

### Locks

```sql
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

```sql
CREATE USER youruser;
\du

-- new session
psql -U youruser -d supertest_lab
SELECT * FROM people;

-- original session
GRANT ALL ON people TO youruser;

-- switch sessions again
SELECT * FROM people;

```

### 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;`