understanding case when then end keywords

Author: techysanoj

as_keyword.sql

@@ -8,3 +8,9 @@ select * from film; -- here we can change our sql statement accordingly
 
 select * from newFilm;
 
+
+create table newFilm2
+AS
+select film_id, title, release_year from film;
+
+select * from newFilm2;

case_when_then_end_keywords.sql

@@ -0,0 +1,43 @@
+use sakila;
+
+show tables;
+
+select * from customer;
+
+-- all these keywords must be used together
+-- so its kind of basically giving the classification to the column values
+
+select 
+customer_id,
+first_name,
+last_name,
+CASE
+WHEN address_id > 100 THEN 'Address is greather than 100'
+ WHEN address_id < 100 THEN 'Address is less than 100'
+ WHEN address_id = 100 THEN 'Address is equal to 100'
+END as address_id_range
+from customer; -- now according to the value of the address_id the column will show this kind of output
+
+
+-- we can also use this in where clause accordingly
+select * from city;
+
+select * from city 
+where country_id = 
+(
+CASE
+WHEN country_id in (82,87, 101, 60) then country_id
+ WHEN country_id NOT IN (82, 87, 101, 60) then 90
+END
+); -- here all those country_id follows the first case there result will be shown
+
+
+-- in order by clause also
+select * from city 
+order by
+(
+CASE
+WHEN country_id in (82,87, 101, 60) then city
+ WHEN country_id NOT IN (82, 87, 101, 60) then country_id
+END
+);