Schema Notes

Temporary Tables and Session Scope

A real table that exists only for your session. Learn CREATE TEMPORARY TABLE, its scope and lifetime, indexing it, and the dialect differences.

SQL

Schema Design: Entities, Attributes and Relationships

How to get from a description of a business to a set of tables: find the entities, give them attributes, connect them, and name everything consistentl...

SQL

NOT NULL, DEFAULT, UNIQUE and CHECK

The four constraints that guard a single table. What each one enforces, how NULL interacts with UNIQUE and CHECK, and why the database is the right pl...

SQL

ALTER TABLE: Adding, Modifying and Removing Columns

ALTER changes a table that already holds data. Add and drop columns, change types, set defaults and manage constraints without losing rows.

SQL

CREATE: Databases, Schemas and Tables

CREATE defines the objects data lives in. Learn CREATE DATABASE, CREATE SCHEMA and CREATE TABLE, with column definitions and inline constraints.

SQL

SQL Data Types Explained

Numeric, string, date and boolean types across the major dialects, and how to pick the type that stops bad data at the door.

SQL

The Relational Model: Tables, Rows, Columns and Schemas

Tables hold typed columns and unordered rows, schemas hold tables, and every value obeys the type its column declares.