SQL WHERE Clause

The WHERE clause filters rows, keeping only those that meet a condition. Without it you get every row in the table; with it you get exactly the rows your question is about.

Syntax

SELECT column1, column2
FROM table_name
WHERE condition;

Comparison operators

Examples

1. Filter on text

All delivered orders:

SELECT order_id, customer_id, order_date
FROM orders
WHERE status = 'Delivered'
LIMIT 5;

Result:

(5 rows)

Text values go in single quotes, and in PostgreSQL the match is case-sensitive.

2. Filter on numbers

Products priced above ₹5,000:

SELECT product_name, price
FROM products
WHERE price > 5000;

Result:

(3 rows)

3. Filter on dates

Orders placed on or after 1 January 2026:

SELECT order_id, order_date, status
FROM orders
WHERE order_date >= '2026-01-01';

Result:

(3 rows)

Write dates as 'YYYY-MM-DD'. This format works in every major database.

4. Combine conditions with AND

AND keeps rows where both conditions are true. Prime customers in Karnataka:

SELECT customer_name, city
FROM customers
WHERE is_prime = TRUE
  AND state = 'Karnataka';

Result:

(1 row)

5. Either condition with OR

OR keeps rows where at least one condition is true. Orders that were cancelled or returned:

SELECT order_id, status
FROM orders
WHERE status = 'Cancelled'
   OR status = 'Returned';

Result:

(4 rows)

6. Exclude rows with NOT

Every order that is not delivered:

SELECT order_id, status
FROM orders
WHERE NOT status = 'Delivered';

Result:

(8 rows)

WHERE status <> 'Delivered' gives the same result.

AND, OR and brackets

AND is evaluated before OR, just as multiplication comes before addition. This catches a lot of people out. Suppose you want UPI or Card orders that were delivered:

-- Wrong: AND binds first, so this means UPI orders (any status) OR delivered Card orders
SELECT COUNT(*) AS orders
FROM orders
WHERE payment_method = 'UPI' OR payment_method = 'Card'
  AND status = 'Delivered';

Result:

(1 row)

-- Right: brackets make the intent explicit
SELECT COUNT(*) AS orders
FROM orders
WHERE (payment_method = 'UPI' OR payment_method = 'Card')
  AND status = 'Delivered';

Result:

(1 row)

Different answers from almost the same query. Always use brackets when you mix AND and OR.

Common mistakes

• Double quotes around text. WHERE city = "Delhi" makes PostgreSQL look for a column named Delhi.
• Comparing with NULL using =. WHERE phone = NULL never matches anything. Use IS NULL (see the NULL lesson).
• Mixing AND/OR without brackets, as shown above.

Practice question

Find all products in category 1 (Electronics) that cost less than ₹30,000 and have more than 30 units in stock.

SELECT product_name, price, stock_qty
FROM products
WHERE category_id = 1
  AND price < 30000
  AND stock_qty > 30;

Key takeaways

• WHERE filters rows before anything else is calculated.
• Use comparison operators for numbers, text and dates.
• AND needs every condition true; OR needs at least one.
• AND runs before OR, so add brackets when mixing them.