Day 02: Datatypes, Primary Key and Constraints

```# Datatypes An attribute that specifies the type of data in a column of our database - table.

Most widely used are:

• Numerical -> INT DOUBLE FLOAT DECIMAL
• String -> VARCHAR
• Date -> DATE
• Boolean -> BOOLEAN

Primary Key🔑

• The PRIMARY KEY constraint uniquely indentifies each record in a table.
• Primary keys must contain UNIQUE values, and cannot contain NULL values.
• A table can have only ONE primary key.

NOT NULL

CREATE TABLE customers
(
    acc_id INT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    acc_type VARCHAR(50) NOT NULL DEFAULT 'Savings'
);

AUTO_INCREMENT

is achieved using either Identity Columns or the legacy SERIAL pseudo-type, which utilize internal database sequences to automatically generate unique, sequential numeric values when new rows are inserted.

CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    firstname VARCHAR(50),
    lastname VARCHAR(50)
);