lesson 03 Filtering & sorting · beginner

Filter with WHERE

Keep only rows that meet a condition.

the idea

WHERE keeps only rows whose condition is true. Text values go in single quotes and must match exactly. The filter runs before the SELECT list is produced, so you can filter on a column you do not return.

Dataset: Retail

The tables the challenges use, with their first 6 rows. Under each column name: the kind of value it holds, and which table it links to.

worked example

Run these steps in order to see the idea before you write your own query. The step marked “the pattern” is what the challenges ask for. Running the example does not count toward progress.

1. 1

   Preview the column you will filter. Run this. order_type tells you whether a row is a sale, cancellation, or adjustment.

   step-1.sql Run

   sql›

   SELECT order_id, invoice_no, order_type
   FROM orders
   LIMIT 10;

2. 2

   Filter to one country. Run this. WHERE keeps only orders where country is Netherlands.the pattern

   example.sql Run

   sql›

   SELECT order_id, invoice_no, ordered_at
   FROM orders
   WHERE country = 'Netherlands';

common mistake

Double quotes name columns in SQL. WHERE order_type = "sale" compares with a column named sale, not with the text 'sale'.