-- NOTE: this is for SQL-Oracle specifically
/*
NB: Please like Mingles444 post, I derived this from him/her
*/
-- syntax: (Retrieved from grepper:Mingles444)
CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN conditionN THEN resultN
ELSE result
END
-- example:
SELECT
CASE
WHEN (1+6 = 6) THEN 'A'
WHEN (1+6 = 7) THEN 'B'
WHEN (1+6 = 8) THEN 'C'
ELSE 'D'
END
FROM DUAL;
-- OUTPUT: B
SELECT customer_id, first_name,
CASE
WHEN country = 'USA' THEN 'United States of America'
WHEN country = 'UK' THEN 'United Kingdom'
ELSE 'Unknown Country'
END AS country_name
FROM Customers;
Change query output depending on conditions.
Example: Returns users and their subscriptions, along with a new column
called activity_levels that makes a judgement based on the number of
subscriptions.
SELECT first_name, surname, subscriptions
CASE WHEN subscriptions > 10 THEN 'Very active'
WHEN Quantity BETWEEN 3 AND 10 THEN 'Active'
ELSE 'Inactive'
END AS activity_levels
FROM users;
/*CASE statements are used to create different outputs and is
used by SQL as a way to handle if-then logic.*/
SELECT column_name,
CASE
WHEN condition THEN 'Result_1'
WHEN condition THEN 'Result_2'
ELSE 'Result_3'
END
FROM table_name;
SELECT order_id, customer_id,
CASE
WHEN amount >= 400 THEN (amount - amount * 10/100)
END AS offer_price
FROM Orders;
-- Case Eg.) to retrive the MAX value of a Field
-- if there are entries for the Field in table MAX value will be returned
-- But if there is no entries at all for the Field in tabel MAX will return
-- Null as the output. But Using Case When we can check it out return zero
-- or any other value if there is no enties for the Field in table..
SELECT
CASE -- Like Switch Case
WHEN -- First When condition
(MAX(BILLID) IS NULL) -- Condition
THEN 1 -- output (We can also add more When conditions like Above)
ELSE -- When WHEN Condition not Satisfied Below will be Executed.
(MAX(BILLID)) -- output
END
as MAXBILLID from DUAL;
-- Final Output
-- If there is no entry in the Field for the table
-- BILLID
-- 1
-- If there are entries MAX of that Field value from the table
-- BILLID
-- 10
SELECT customer_id, first_name,
CASE
WHEN age >= 18 THEN 'Allowed'
END AS can_vote
FROM Customers;
Case Statement basically
Like IF - THEN - ELSE statement.
The CASE statement goes through conditions
and returns a value when the
first condition is met and
once a condition is true,
it will stop reading and return the result.
If no conditions are true,
it returns the value in the ELSE clause.
If there is no ELSE part and
no conditions are true, it returns NULL.
FOR EXAMPLE =
CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN conditionN THEN resultN
ELSE result
END
-- example:
SELECT
CASE
WHEN (1+6 = 6) THEN 'A'
WHEN (1+6 = 7) THEN 'B'
WHEN (1+6 = 8) THEN 'C'
ELSE 'D'
END
FROM DUAL;
Result would be 'B' since it is the first
correct answer