Database Definition Language

Introduction

What is a Database Definition Language?

This is the programming language used to construct and alter the design of tables contained within a database. The most common form of DDL is Structured Query Language(SQL).

This language is not used to directly alter the data stored within a table, rather it is used to construct the framework within which data is contained.

 

 

 

CREATE TABLE

CREATE TABLE COMMAND

Example 1 – Simple Non Relational Table

CREATE TABLE users(firstname text, lastname text, age integer, date of birth date);

Example 2 – Create a table with a primary key

 

Example 3 – Create another table that references the primary from the other table

 

SQL Data Types

  • Char – Fixed Length Text
  • Varchar(255) – Variable Length (For SQLite use – Text)
  • Integer – Store a whole number
  • Boolean – Stores 1 or 0 for Boolean
  • Real – Floating point number
  • Date / Time – (SQLite has no date  or time data type so use Text / Float / Integer and use something like Epoch Time)

ALTER TABLE

ALTER TABLE COMMAND

Examples:

ALTER TABLE username ADD COLUMN height real;

ALTER TABLE username MODIFY COLUMN height integer

ALTER TABLE username DROP COLUMN email;

 

DROP TABLE

DROP TABLE COMMAND

DROP TABLE users;