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←Reading data: SELECT
Lesson 2 / 8

Module 01 · lesson 2

Selecting only the columns you need

The founder needs a price list — just the name and price of each product. Dates and stock levels are unnecessary here. Pulling the whole table for two columns is wasteful.

You'll need:SELECT and FROM: getting data out(opens in a new tab)

List the columns you need

Instead of *, name the columns you need, separated by commas — and in exactly the order you want to see them:

SELECT category, stock
FROM products;

This query returns only two columns — category and stock.

Projection

Selecting specific columns is called projection. In real queries you almost always do this — it's:

  • faster — the database doesn't drag along extra data;
  • more readable — it's immediately clear what's needed;
  • more reliable — the query won't "drift" if new columns are added to the table.

So an explicit list is almost always better than *.

Your turn

Put together a price list: output the name and price of each product.

Summary

  • A comma-separated list of columns returns only what you need — in the order you give. This is projection.
  • The column order in SELECT = the order in the result.
  • An explicit list beats * (faster, more readable, more reliable).