Changing data: INSERT, UPDATE, DELETE डेटा बदलना: INSERT, UPDATE, DELETE

1. Adding a row with INSERT

So far we only read data. INSERT adds a new row:

INSERT INTO products (id, name, category, price) VALUES (16, 'Poha 500g', 'Grocery', 35);

List the columns, then the values in the same order. Text in single quotes, numbers without.

Don’t worry: every Run starts from a fresh copy of the sample database, so you can experiment freely. Add a SELECT after your INSERT to see the new row.

                INSERT INTO products
  (id, name, category, price)
VALUES (16, 'Poha 500g', 'Grocery', 35);
SELECT * FROM products;
              

Challenge: A new item on the shelf

The shop starts selling a new item. Insert a row into products with id 16, name Jaggery 1kg, category Grocery and price 70.

2. UPDATE and DELETE — always with WHERE

UPDATE changes values in existing rows, DELETE removes rows:

• UPDATE products SET price = 50 WHERE id = 4;
• DELETE FROM sales WHERE id = 7;

Golden rule: always write the WHERE. UPDATE products SET price = 50; without WHERE changes every product’s price, and DELETE FROM sales; empties the whole table! In a real shop’s database there is no undo button. Run a SELECT with the same WHERE first to check which rows you will touch.

                UPDATE products
SET price = 50
WHERE id = 4;
SELECT * FROM products
WHERE id = 4;
              

Challenge: Milk price up, one sale returned

Two jobs: (1) milk now costs more — set price to 70 for the product with id 9. (2) The customer of sale id 22 returned the tea — delete that row from sales. Change nothing else.