Hello, World in SQL

Run your first query and get familiar with tools.

Connect to a database

• Postgres: psql postgresql://user:pass@localhost:5432/db
• MySQL: mysql -h 127.0.0.1 -u user -p db
• SQLite: sqlite3 db.sqlite
• GUI options: DBeaver, TablePlus, DataGrip, psql/pgcli

First query

-- Create a sample table
CREATE TABLE IF NOT EXISTS users (
  id SERIAL PRIMARY KEY,
  name TEXT NOT NULL,
  email TEXT UNIQUE
);

-- Insert a row
INSERT INTO users (name, email) VALUES ('Ada', 'ada@example.com');

-- Read rows
SELECT id, name, email FROM users;

The exact DDL/DDL types vary per engine, but SELECT syntax is broadly portable.

Result set basics

• Columns have names and types
• Rows are ordered only if you specify ORDER BY
• NULL means “unknown/missing”, not zero or empty

Tools and workflows

• Keep queries in version control (.sql files)
• Use transactions when changing data (BEGIN; ... COMMIT;)
• Favor parameterized queries in application code to prevent injection

Summary

• Connect, create a table, insert, then SELECT
• Results are unordered without ORDER BY; treat NULL carefully