CONCATenate columns to a surrogate key

Another strategy to add a surrogate key to an existing table is to concatenate existing columns with the CONCAT() function.

Let's think of the following example table:

CREATE TABLE cars (
 make varchar(64) NOT NULL,
 model varchar(64) NOT NULL,
 mpg integer NOT NULL
)

The table is populated with 10 rows of completely fictional data.

Unfortunately, the table doesn't have a primary key yet. None of the columns consists of only unique values, so some columns can be combined to form a key.

In the course of the following exercises, you will combine make and model into such a surrogate key.

Bu egzersiz

Introduction to Relational Databases in SQL

kursunun bir parçasıdır

Kursu Görüntüle

Uygulamalı interaktif egzersiz

Bu örnek kodu tamamlayarak bu egzersizi bitirin.

-- Count the number of distinct rows with columns make, model
___
FROM cars;

Kodu Düzenle ve Çalıştır