Count Length of Digits Per Column Per Row

Question

I generated the following table:

CREATE table user (  
    user_id INT NOT NULL UNIQUE AUTO_INCREMENT,  
    user_phone_number INT,  
    user_city VARCHAR(32) NOT NULL,  
    PRIMARY KEY (user_id)
);

And I'm being asked the following: number of users per length of the phone number (number of numeric digits)

I try the following:

SELECT LENGTH(user_phone_number)
FROM user
WHERE user is not null
GROUP BY user_phone_number);

but if there are several users with the same phone number length it repeats them in several rows instead of providing the Total per length. Please help

Answer 1

You have two problems with your SQL. The most obvious is that you have left out the COUNT() . This is important if you want to count something.

The second is that the SELECT column and the GROUP BY column don't match. These should (almost always) be the same:

SELECT LENGTH(user_phone_number), COUNT(*)
FROM user
WHERE user_phone_number is not null
GROUP BY LENGTH(user_phone_number);

You probably want an ORDER BY LENGTH(user_phone_number) at the end.