how use case in mysql code example

Example: mysql case

-- LABEL MOVIE LENGTH 
select title, length,
CASE 
	 when length < 50 then 'very short film'
     when length < 90 then 'short film'
     when length < 120 then 'medium length film'
     when length > 120 then 'long film'
     else 'unknown length'
END -- AS film_length
from film;

-- SAME AS ABOVE BUT ON A CUSTOM NAMED COLUMN
select title, length,
CASE 
	 when length < 50 then 'very short film'
     when length < 90 then 'short film'
     when length < 120 then 'medium length film'
     when length > 120 then 'long film'
     else 'unknown length'
END  AS film_length
from film;

-- RESULT
+-----------------------------+--------+--------------------+
| title                       | length | film_length        |
+-----------------------------+--------+--------------------+
| ACADEMY DINOSAUR            |     86 | short film         |
| ACE GOLDFINGER              |     48 | very short film    |
| ADAPTATION HOLES            |     50 | short film         |
| AFFAIR PREJUDICE            |    117 | medium length film |
| AFRICAN EGG                 |    130 | long film          |
| AGENT TRUMAN                |    169 | long film          |
| AIRPLANE SIERRA             |     62 | short film         |
| AIRPORT POLLOCK             |     54 | short film         |
| ALABAMA DEVIL               |    114 | medium length film |
| ALADDIN CALENDAR            |     63 | short film         |
| ALAMO VIDEOTAPE             |    126 | long film          |
| ALASKA PHANTOM              |    136 | long film          |
| ALI FOREVER                 |    150 | long film          |
| ALICE FANTASIA              |     94 | medium length film |
| ALIEN CENTER                |     46 | very short film    |