# SQL COURSE
## What is a databse?
- A collection of data
- A structured set of computeerized data with an accessible interface

### SQL vs. MySQL
- SQL is the language used to talk to databases
- Relational databases use SQL
- Examples of relational database management systems: MySQL, SQLite, PostgreSQL

### Entering MySQL in terminal
- `mysql -u root -p`

### Database creation/removal:
`CREATE DATABASE <name>;` Creates a new databse
`DROP DATABASE <name>;` Deletes a database
`USE DATABASE <name>;` Selects a databse for use (where you'ree working)
`SELECT database()` Shows which database we are using

### Table Creation
Creating a table:
```SQL
CREATE TABLE tablename
(
  name VARCHAR(100),
  age INT
);
```
Creating a table with a default value:

```SQL
CREATE TABLE tablename
(
  name VARCHAR(100) DEFAULT 'unnamed',
  age INT DEFAULT 999
);
```
Creating a table without allowing for null:

```SQL
CREATE TABLE tablename
(
  name VARCHAR(100) NOT NULL DEFAULT 'unnamed',
  age INT NOT NULL DEFAULT 999
);
```
Adding in AUTO_INCREMENT:
```SQL
CREATE TABLE unique_cats2 (
    cat_id INT NOT NULL AUTO_INCREMENT,
    name VARCHAR(100),
    age INT,
    PRIMARY KEY (cat_id)
);
```
### View Tables
`SHOW TABLES`
`DESC <tablename>`
`SHOW COLUMNS FROM <tablename>`

## INSERT
```SQL
INSERT INTO table_name
            (column_name, column_name)
      VALUES(value, value),
            (value, value),
            (value, value);
```
## SQL QUERIES

### SELECT *

Basic query:
```SQL
SELECT *
  FROM customers;
```

Query with where:
```SQL
SELECT *
  FROM customers
    WHERE customerID = 5;
```

Query with return modifier to return (ASC = ascending DESC = Descending):
```SQL
SELECT *
  FROM customers
  ORDER BY customerID DESC;
```

### Aliases
```SQL
SELECT cat_id AS id, name FROM cats;
```