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SQL Lesson 16: Creating tables

Introduction & Core Concept

We now enter Data Definition Language (DDL). To construct brand new table schemas inside a relational database, we write a CREATE TABLE statement defining the primary key, column headers, and structural datatypes.

CREATE TABLE table_name (
  id INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  balance REAL DEFAULT 0.0,
  join_date DATE
);
Core Structural Datatypes
  • INTEGER: Whole numeric numbers without decimals.
  • TEXT (or VARCHAR): Character sequences and text strings.
  • REAL (or DECIMAL / FLOAT): Floating-point decimal numbers.
  • DATE / DATETIME: Calendar timestamps.
    • Why & Where We Use It
  • Why We Use It: Enforces strict structural integrity. Unlike NoSQL document stores where any arbitrary data can be inserted, SQL tables enforce strict schema rules preventing corrupt or malformed data from entering the system.
  • Where We Use It: Initializing application databases, creating temporary audit logging tables, and standing up data warehouse reporting staging tables.
    • Real-World Example

    ShopMart wants to build a new customer support ticketing module. The database architect writes a CREATE TABLE support_tickets query specifying an auto-incrementing ticket ID, customer ID linking key, issue details text block, and a default status of 'Open'.

    Best Practices: What to Do & What NOT to Do
  • What to Do: Always include IF NOT EXISTS in your creation statements (e.g., CREATE TABLE IF NOT EXISTS my_table). This prevents script crash errors if the table was already created during an earlier deployment.
  • What NOT to Do: Do not omit Primary Keys. Every robust relational table should possess a dedicated primary key to ensure row uniqueness and enable high-speed index lookups.
    • Syntax & Pro Tips
    CREATE TABLE IF NOT EXISTS audit_logs (
  log_id INTEGER PRIMARY KEY AUTOINCREMENT,
  action TEXT NOT NULL,
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);
    Interactive Sandboxed Terminal (Preloaded DB Schema: SHOPMART)
    SQL Query WorkspaceSQLite v3.45 (WASM Mode)
    QUICK INSERT:
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