Databases & Tables

Before you can query anything, you need a database to hold it and a table shaped to fit your data. This lesson covers the handful of commands you'll run before writing a single SELECT.

CREATE DATABASE

Creates a new, empty database on the server.

CREATE DATABASE database_name;

CREATE DATABASE CompanyDB;

Reserves a named space for tables, views, and other objects.
Does not select the database for use — you still need to switch to it with USE.

Common Mistake

Creating a database with the same name as an existing one without checking first.

USE

Switches the active database for the current session.

USE database_name;

USE CompanyDB;

All statements that follow run against this database until you switch again.

Common Mistake

Running a query against the wrong database because USE was never called first.

SHOW DATABASES / TABLES

Lists the databases on the server, or the tables inside the current one.

SHOW DATABASES;
SHOW TABLES;

Tables_in_CompanyDB
Employee
Department

A quick way to see what already exists before writing a query against it.

Common Mistake

Assuming SHOW TABLES works identically across every database engine — the exact syntax varies between MySQL, PostgreSQL, and others.

Data Types — a Quick Pointer

Every column is given a type that constrains what it can store and how much room it takes.

Numbers, text, dates, and flags each have their own type family.
The next lesson covers sizing each of them for a real, memory-conscious schema — not just which type to use, but which specific size.

With a database and the idea of typed columns in place, the next lesson goes deep on choosing the right type and size for every column you'll ever define.