# Calling all beginners: simple SQL challenge

Hi!

Here's a little challenge for beginners.

We have a `users` table and we need to know *the number of users in 3 age ranges*.

* if age < 18 then age range is `minor`.
* if age < 65 then age range is `adult`.
* if age >= 65 then age range is `senior`.
    
## Table structure
```sql
CREATE TABLE users (
  id int NOT NULL AUTO_INCREMENT,
  age SMALLINT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB;
```

## Sample data
```sql
INSERT INTO users(age)
VALUES
(2), (4), (6),
(12), (14), (16), (21), (25),
(27), (31), (33), (37), (39),
(57), (57), (59), (61), (63), (65)
;
```

## Expected results
```plaintext
| ageRange | nb     |
| -------- | ------ |
| 6        | minor  |
| 12       | adult  |
| 1        | senior |
```

Go ahead and give it a try!

You might want to read about the following statements: `IF`, `CASE/WHEN` and `GROUP BY`.

## A possible solution
Note that I'm using MySQL but since it is standard SQL you should be able to port it to another DB engine.

First we need to determine age ranges and for that we're going to add a [CASE statement](https://dev.mysql.com/doc/refman/8.0/en/case.html).

```sql
CASE
    WHEN age < 18 THEN 'minor'
    WHEN age < 65 THEN 'adult'
    ELSE 'senior'
END as ageRange
```

Pretty straightforward, right? We could have used two `IF` statements but I opted for `CASE/WHEN` as I find it elegant. :)

Add that to a `SELECT` statement and you get users' age along with their age group.

Next we need to count how many users belong to each group. It's as simple as adding a `GROUP BY ageRange` clause.

```sql
SELECT
    count(*),
    CASE
        WHEN age < 18 THEN 'minor'
        WHEN age < 65 THEN 'adult'
        ELSE 'senior'
    END as ageRange
FROM users
GROUP BY ageRange
```

And we're done!

Happy coding!