SQL SELECT Statement

The SELECT statement reads data from a table. You list the columns you want after SELECT and the table after FROM. Every analysis you'll ever write in SQL starts here.

Syntax

SELECT column1, column2, ...
FROM table_name;

Examples

1. Select specific columns

Show each product's name and price:

SELECT product_name, price
FROM products;

Result:

(showing 12 of 15 rows)

2. Select all columns with *

SELECT *
FROM categories;

Result:

(6 rows)

* is great for a first look at a table. Combine it with LIMIT on big tables so you don't pull millions of rows.

3. Calculated columns

You can do arithmetic inside SELECT. Here is the profit per unit on each product:

SELECT product_name,
       price,
       cost_price,
       price - cost_price AS profit_per_unit
FROM products
LIMIT 5;

Result:

(5 rows)

The new column only exists in the output. The table itself is not changed. AS profit_per_unit gives the column a readable name (you'll learn more about aliases in the next lesson).

4. Line revenue for each order item

SELECT order_id,
       product_id,
       quantity,
       unit_price,
       quantity * unit_price AS gross_amount
FROM order_items
LIMIT 5;

Result:

(5 rows)

5. Constants and expressions without a table

PostgreSQL lets you run SELECT without FROM, which works like a calculator:

SELECT 23999 * 0.18 AS gst_amount, 'ShopKart' AS store;

Result:

(1 row)

How SQL runs a SELECT

Even though you write SELECT first, the database reads FROM first: it finds the table, then picks the columns. This logical order becomes important later:

1. FROM → which table(s)

2. WHERE → which rows

3. GROUP BY → how to group

4. HAVING → which groups

5. SELECT → which columns and calculations

6. ORDER BY → sort

7. LIMIT → how many rows

Common mistakes

Misspelled column names. The error tells you exactly which one:

SELECT product_nme FROM products;

Error: column "product_nme" does not exist

• Trailing comma before FROM. SELECT product_name, price, FROM products is a syntax error.
• Using SELECT * in reports. List columns explicitly: it's clearer and avoids surprises when the table changes.

Practice question

Show each product's name, its price, and its price including 18% GST as a column called price_with_gst.

SELECT product_name,
       price,
       price * 1.18 AS price_with_gst
FROM products
LIMIT 5;

Key takeaways

• SELECT picks columns; FROM names the table.
• * returns all columns; use it for exploration, not reports.
• You can calculate new columns with arithmetic and name them with AS.
• The database processes FROM before SELECT.