Combining tables manually is time-consuming. Luckily, SQL gives us an easy sequence for this: it’s called a
If we want to combine
customers, we would type:
SELECT * FROM orders JOIN customers ON orders.customer_id = customers.customer_id;
Let’s break down this command:
- The first line selects all columns from our combined table. If we only want to select certain columns, we can specify which ones we want.
- The second line specifies the first table that we want to look in,
- The third line uses
JOINto say that we want to combine information from
- The fourth line tells us how to combine the two tables. We want to match
Because column names are often repeated across multiple tables, we use the syntax
table_name.column_name to be sure that our requests for columns are unambiguous. In our example, we use this syntax in the
ON statement, but we will also use it in the
SELECT or any other statement where we refer to column names.
For example: Instead of selecting all the columns using
*, if we only wanted to select
order_id column and
customer_name column, we could use the following query:
SELECT orders.order_id, customers.customer_name FROM orders JOIN customers ON orders.customer_id = customers.customer_id;
orders table and
subscriptions table and select all columns.
Make sure to join on the
Don’t remove the previous query.
Add a second query after your first one that only selects rows from the join where
description is equal to ‘Fashion Magazine’.