INSERT, UPDATE, DELETE

Adding Data With INSERT

INSERT INTO customers (name, email, city) VALUES
  ('Priya Sharma', 'priya@example.com', 'Mumbai');

INSERT INTO customers (name, email, city) VALUES
  ('Rahul Patel', 'rahul@example.com', 'Pune'),
  ('Anjali Rao', 'anjali@example.com', 'Hyderabad');

Updating Data

UPDATE customers SET city = 'Bengaluru' WHERE id = 1;
UPDATE customers SET city = 'Pune', updated_at = NOW() WHERE email = 'rahul@example.com';

Never run UPDATE without a WHERE clause unless you really mean every row.

Deleting Data

DELETE FROM customers WHERE id = 3;
DELETE FROM customers WHERE is_inactive = TRUE;

Copying Between Tables

INSERT INTO vip_customers (name, email)
SELECT name, email FROM customers WHERE total_spend > 1000;

Managing Conflicts (Upsert)

• PostgreSQL: ON CONFLICT (email) DO UPDATE SET ...
• MySQL: ON DUPLICATE KEY UPDATE ...
• SQLite: ON CONFLICT ... (Postgres-style).
• Oracle / SQL Server: MERGE statement.

Key Points

• INSERT adds rows; UPDATE changes them; DELETE removes them.
• Always pair UPDATE/DELETE with a WHERE clause.
• INSERT ... SELECT copies data between tables.
• Each database offers an upsert mechanism; they differ slightly.