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DQDigital Qasas Courses/SQL for Professionals
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  • What SQL is, and why professionals learn it
  • Learn faster: pair this course with a free AI assistant
  • SELECT and FROM: your first real query
  • WHERE: keep only the rows you want
  • Combine conditions: AND, OR, IN, BETWEEN, LIKE, NULL
  • ORDER BY, LIMIT, and DISTINCT
  • COUNT, SUM, AVG, MIN, MAX
  • GROUP BY: one number per group
  • HAVING: filter the groups
  • Why tables relate: keys and joins
  • INNER JOIN: matching rows from two tables
  • LEFT JOIN: keep everything, find what is missing
  • Subqueries: a query inside a query
  • CASE: if-and-then inside a query
  • Window functions: a first look
  • Putting it together, and a cheat sheet
  • Practice challenges
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CASE: if-and-then inside a query

Last updated 14 June 2026

CASE is SQL's if-and-then. It checks conditions in order and returns the first value that matches. Use it to bucket numbers into labels or to relabel codes.

SELECT name, price,
  CASE
    WHEN price >= 500 THEN 'premium'
    WHEN price >= 150 THEN 'standard'
    ELSE 'entry'
  END AS tier
FROM products;

Label each product by price tier.

CREATE TABLE customers (
  id INTEGER PRIMARY KEY,
  name TEXT,
  city TEXT,
  signup_date TEXT
);
INSERT INTO customers VALUES
  (1, 'Aisyah Rahman', 'Kuala Lumpur', '2023-01-12'),
  (2, 'Lim Wei Jie', 'Penang', '2023-02-03'),
  (3, 'Arjun Pillai', 'Johor Bahru', '2023-02-20'),
  (4, 'Nurul Huda', 'Kuala Lumpur', '2023-03-15'),
  (5, 'Tan Mei Ling', 'Ipoh', '2023-05-01'),
  (6, 'Faiz Hassan', 'Penang', '2023-06-10');

CREATE TABLE products (
  id INTEGER PRIMARY KEY,
  name TEXT,
  category TEXT,
  price REAL
);
INSERT INTO products VALUES
  (1, 'Standard License', 'Software', 199.0),
  (2, 'Pro License', 'Software', 499.0),
  (3, 'Onboarding Workshop', 'Service', 1200.0),
  (4, 'Support Plan', 'Service', 300.0),
  (5, 'Data Pack', 'Add-on', 89.0);

CREATE TABLE orders (
  id INTEGER PRIMARY KEY,
  customer_id INTEGER,
  order_date TEXT,
  status TEXT
);
INSERT INTO orders VALUES
  (1001, 1, '2023-03-01', 'paid'),
  (1002, 1, '2023-04-12', 'paid'),
  (1003, 2, '2023-04-15', 'paid'),
  (1004, 3, '2023-05-02', 'refunded'),
  (1005, 4, '2023-05-20', 'paid'),
  (1006, 2, '2023-06-01', 'pending'),
  (1007, 5, '2023-06-18', 'paid');

CREATE TABLE order_items (
  order_id INTEGER,
  product_id INTEGER,
  quantity INTEGER
);
INSERT INTO order_items VALUES
  (1001, 1, 2), (1001, 5, 1),
  (1002, 2, 1),
  (1003, 1, 1), (1003, 4, 1),
  (1004, 3, 1),
  (1005, 2, 2), (1005, 5, 3),
  (1006, 1, 1),
  (1007, 3, 1), (1007, 4, 2);
SELECT name, price,
  CASE
    WHEN price >= 500 THEN 'premium'
    WHEN price >= 150 THEN 'standard'
    ELSE 'entry'
  END AS tier
FROM products;

A neat trick: a CASE inside SUM counts only the rows that match a condition. This counts paid versus refunded orders in one row.

CREATE TABLE customers (
  id INTEGER PRIMARY KEY,
  name TEXT,
  city TEXT,
  signup_date TEXT
);
INSERT INTO customers VALUES
  (1, 'Aisyah Rahman', 'Kuala Lumpur', '2023-01-12'),
  (2, 'Lim Wei Jie', 'Penang', '2023-02-03'),
  (3, 'Arjun Pillai', 'Johor Bahru', '2023-02-20'),
  (4, 'Nurul Huda', 'Kuala Lumpur', '2023-03-15'),
  (5, 'Tan Mei Ling', 'Ipoh', '2023-05-01'),
  (6, 'Faiz Hassan', 'Penang', '2023-06-10');

CREATE TABLE products (
  id INTEGER PRIMARY KEY,
  name TEXT,
  category TEXT,
  price REAL
);
INSERT INTO products VALUES
  (1, 'Standard License', 'Software', 199.0),
  (2, 'Pro License', 'Software', 499.0),
  (3, 'Onboarding Workshop', 'Service', 1200.0),
  (4, 'Support Plan', 'Service', 300.0),
  (5, 'Data Pack', 'Add-on', 89.0);

CREATE TABLE orders (
  id INTEGER PRIMARY KEY,
  customer_id INTEGER,
  order_date TEXT,
  status TEXT
);
INSERT INTO orders VALUES
  (1001, 1, '2023-03-01', 'paid'),
  (1002, 1, '2023-04-12', 'paid'),
  (1003, 2, '2023-04-15', 'paid'),
  (1004, 3, '2023-05-02', 'refunded'),
  (1005, 4, '2023-05-20', 'paid'),
  (1006, 2, '2023-06-01', 'pending'),
  (1007, 5, '2023-06-18', 'paid');

CREATE TABLE order_items (
  order_id INTEGER,
  product_id INTEGER,
  quantity INTEGER
);
INSERT INTO order_items VALUES
  (1001, 1, 2), (1001, 5, 1),
  (1002, 2, 1),
  (1003, 1, 1), (1003, 4, 1),
  (1004, 3, 1),
  (1005, 2, 2), (1005, 5, 3),
  (1006, 1, 1),
  (1007, 3, 1), (1007, 4, 2);
SELECT
  SUM(CASE WHEN status = 'paid' THEN 1 ELSE 0 END) AS paid,
  SUM(CASE WHEN status = 'refunded' THEN 1 ELSE 0 END) AS refunded
FROM orders;

Your turn

Add a column called kind to the customers list that reads 'KL' when the city is Kuala Lumpur and 'Other' otherwise. Return name, city, and kind.

Flag the Kuala Lumpur customers with a CASE column.

CREATE TABLE customers (
  id INTEGER PRIMARY KEY,
  name TEXT,
  city TEXT,
  signup_date TEXT
);
INSERT INTO customers VALUES
  (1, 'Aisyah Rahman', 'Kuala Lumpur', '2023-01-12'),
  (2, 'Lim Wei Jie', 'Penang', '2023-02-03'),
  (3, 'Arjun Pillai', 'Johor Bahru', '2023-02-20'),
  (4, 'Nurul Huda', 'Kuala Lumpur', '2023-03-15'),
  (5, 'Tan Mei Ling', 'Ipoh', '2023-05-01'),
  (6, 'Faiz Hassan', 'Penang', '2023-06-10');

CREATE TABLE products (
  id INTEGER PRIMARY KEY,
  name TEXT,
  category TEXT,
  price REAL
);
INSERT INTO products VALUES
  (1, 'Standard License', 'Software', 199.0),
  (2, 'Pro License', 'Software', 499.0),
  (3, 'Onboarding Workshop', 'Service', 1200.0),
  (4, 'Support Plan', 'Service', 300.0),
  (5, 'Data Pack', 'Add-on', 89.0);

CREATE TABLE orders (
  id INTEGER PRIMARY KEY,
  customer_id INTEGER,
  order_date TEXT,
  status TEXT
);
INSERT INTO orders VALUES
  (1001, 1, '2023-03-01', 'paid'),
  (1002, 1, '2023-04-12', 'paid'),
  (1003, 2, '2023-04-15', 'paid'),
  (1004, 3, '2023-05-02', 'refunded'),
  (1005, 4, '2023-05-20', 'paid'),
  (1006, 2, '2023-06-01', 'pending'),
  (1007, 5, '2023-06-18', 'paid');

CREATE TABLE order_items (
  order_id INTEGER,
  product_id INTEGER,
  quantity INTEGER
);
INSERT INTO order_items VALUES
  (1001, 1, 2), (1001, 5, 1),
  (1002, 2, 1),
  (1003, 1, 1), (1003, 4, 1),
  (1004, 3, 1),
  (1005, 2, 2), (1005, 5, 3),
  (1006, 1, 1),
  (1007, 3, 1), (1007, 4, 2);
SELECT name, city,
  CASE WHEN  THEN 'KL' ELSE 'Other' END AS kind
FROM customers;
SELECT name, city, CASE WHEN city = 'Kuala Lumpur' THEN 'KL' ELSE 'Other' END AS kind FROM customers;
CASE stops at the first WHEN that is true and ignores the rest. Order the conditions from most specific to least, or a broad early branch will swallow the ones below it.

When several WHEN conditions are true, which one does CASE use?

  • The first true condition, reading top to bottom
  • The last true condition
  • All of them, combined
CASE evaluates branches in order and returns the first match. That is why specific conditions go above general ones.
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