lesson 03 Filtering & sorting · beginner

Filter with WHERE

Keep only rows that meet a condition.

the idea

WHERE keeps rows for which a condition is true. Text values need single quotes; column names do not. Rows whose comparison evaluates to NULL are not kept.

tables in this lesson

The challenges use this data. Each column shows its type underneath; → marks a link to another table.

example

The idea in one query. Press Run to see what it returns; running examples never affects your progress.

SELECT name, city
FROM customers
WHERE city = 'Chicago';

Watch for: SQL uses = for equality. City names are string values, so quote them.

build it step by step

Each step changes one thing. Run them in order and watch the result change.

1. 1

   Start with customers. Chicago and Austin are values, not column names.

   step-1.sql Run

   sql›

   SELECT name,city
   FROM customers;

2. 2

   Keep matching rows. WHERE keeps true comparisons. Missing city values do not match.

   step-2.sql Run

   sql›

   SELECT name,city
   FROM customers
   WHERE city='Chicago';