diff --git a/.vscode/settings.json b/.vscode/settings.json
index 375aedb..62fdbf9 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -26,7 +26,7 @@
       "port": 3306,
       "driver": "MySQL",
       "name": "mysql",
-      "database": "default",
+      "database": "gym",
       "username": "root",
       "askForPassword": true
     },
@@ -36,7 +36,7 @@
       "port": 5432,
       "driver": "PostgreSQL",
       "name": "postgresql",
-      "database": "default",
+      "database": "gym",
       "username": "postgres",
       "askForPassword": true
     }
diff --git a/data/01-mathematical-functions.sql b/data/01-mathematical-functions.sql
new file mode 100644
index 0000000..a18f98e
--- /dev/null
+++ b/data/01-mathematical-functions.sql
@@ -0,0 +1,10 @@
+SELECT price * billing_frequency AS annual_revenue
+FROM memberships;
+
+-- CEIL()
+-- FLOOR()
+-- ROUND()
+-- TRUNC() TRUNCATE() mysql
+
+SELECT TRUNC(consumption, 0) 
+FROM memberships;
diff --git a/data/02-string-functions.sql b/data/02-string-functions.sql
new file mode 100644
index 0000000..62fbcef
--- /dev/null
+++ b/data/02-string-functions.sql
@@ -0,0 +1,25 @@
+SELECT CONCAT(first_name, ' ', last_name)
+FROM memberships;
+
+SELECT CONCAT('$ ', price)
+FROM memberships;
+
+INSERT INTO memberships (
+  membership_start, membership_end, last_checkin, last_checkout,
+  consumption, first_name, last_name, price, billing_frequency, gender)
+VALUES (
+  '2021-10-18', '2021-11-18', '2021-11-01 08:56:01', '2021-11-01 09:20:12',
+  NULL, 'John', 'Doe', 19.99, 12, LOWER('DivErs'));
+
+SELECT * FROM memberships
+WHERE LENGTH(last_name) < 7;
+
+INSERT INTO memberships (
+    membership_start, membership_end, last_checkin, last_checkout,
+  consumption, first_name, last_name, price, billing_frequency, gender)
+VALUES (
+  '2021-05-02', NULL, '2021-06-05 11:52:25', '2021-06-05 11:58:08',
+  NULL, 'Monti', 'Durns', 199.99, 1, TRIM(TRAILING ' ' FROM 'male  ')
+);
+
+SELECT LENGTH(gender) FROM memberships;
diff --git a/data/03-date-time-functions.sql b/data/03-date-time-functions.sql
new file mode 100644
index 0000000..e773548
--- /dev/null
+++ b/data/03-date-time-functions.sql
@@ -0,0 +1,18 @@
+SELECT EXTRACT(MINUTE FROM last_checkin), last_checkin
+FROM memberships;
+
+-- MySQL syntax
+SELECT WEEKDAY(last_checkin) + 1, last_checkin 
+FROM memberships;
+
+-- PostgreSQL syntax
+SELECT EXTRACT(ISODOW FROM last_checkin), last_checkin 
+FROM memberships;
+
+-- MySQL syntax
+SELECT CONVERT(last_checkin, DATE), CONVERT(last_checkin, TIME)
+FROM memberships;
+
+-- PostgreSQL syntax
+SELECT last_checkin::TIMESTAMP::DATE, last_checkin::TIMESTAMP::TIME
+FROM memberships;
diff --git a/data/04-date-time-differences.sql b/data/04-date-time-differences.sql
new file mode 100644
index 0000000..f94cddb
--- /dev/null
+++ b/data/04-date-time-differences.sql
@@ -0,0 +1,11 @@
+-- MySQL syntax
+SELECT TIMESTAMPDIFF(MINUTE, last_checkin, last_checkout)
+FROM memberships;
+
+-- MySQL syntax
+SELECT DATEDIFF(NOW(), membership_start)
+FROM memberships;
+
+-- PostgreSQL syntax
+SELECT NOW() - membership_start
+FROM memberships;
diff --git a/data/05-changing-dates.sql b/data/05-changing-dates.sql
new file mode 100644
index 0000000..3fd03d6
--- /dev/null
+++ b/data/05-changing-dates.sql
@@ -0,0 +1,11 @@
+-- PostgreSQL syntax
+SELECT membership_start + 7, membership_start
+FROM memberships;
+
+-- MySQL syntax
+SELECT DATE_ADD(membership_start, INTERVAL 7 DAY), membership_start
+FROM memberships;
+
+-- PostgreSQL syntax
+SELECT (membership_start + INTERVAL '7 DAY')::TIMESTAMP::DATE, membership_start
+FROM memberships;
diff --git a/data/06-like-pattern-matching.sql b/data/06-like-pattern-matching.sql
new file mode 100644
index 0000000..cf49201
--- /dev/null
+++ b/data/06-like-pattern-matching.sql
@@ -0,0 +1,9 @@
+SELECT first_name LIKE '__o%', first_name
+FROM memberships;
+
+SELECT first_name LIKE 'Ma%', first_name
+FROM memberships;
+
+SELECT first_name
+FROM memberships
+WHERE first_name LIKE 'J____';
diff --git a/data/07-exists-subquery-expressions.sql b/data/07-exists-subquery-expressions.sql
new file mode 100644
index 0000000..f7ea05c
--- /dev/null
+++ b/data/07-exists-subquery-expressions.sql
@@ -0,0 +1,17 @@
+SELECT first_name, last_name
+FROM customers
+WHERE email = 'max@test.com';
+
+SELECT EXISTS(
+  SELECT first_name, last_name
+  FROM customers
+  WHERE email = 'manu@test.com'
+);
+
+SELECT o.id
+FROM orders AS o
+WHERE EXISTS(
+  SELECT c.email
+  FROM customers as c
+  WHERE o.customer_id = c.id AND c.email = 'max@test.com'
+);
diff --git a/data/08-in-subquery-expressions.sql b/data/08-in-subquery-expressions.sql
new file mode 100644
index 0000000..5fda70a
--- /dev/null
+++ b/data/08-in-subquery-expressions.sql
@@ -0,0 +1,19 @@
+SELECT email FROM customers;
+
+SELECT c.email FROM customers AS c
+INNER JOIN orders AS o ON c.id = o.customer_id;
+
+SELECT id
+FROM customers
+WHERE first_name = 'Max' OR first_name = 'Manu';
+
+SELECT id, first_name
+FROM customers
+WHERE first_name IN('Max', 'Manu');
+
+SELECT email
+FROM customers
+WHERE id IN(
+    SELECT customer_id
+    FROM orders
+);
diff --git a/data/09-conditional-expressions.sql b/data/09-conditional-expressions.sql
new file mode 100644
index 0000000..3cf625e
--- /dev/null
+++ b/data/09-conditional-expressions.sql
@@ -0,0 +1,21 @@
+SELECT amount_billed,
+  CASE WHEN amount_billed > 15 AND amount_billed <= 30 THEN 'Normal Day'
+    WHEN amount_billed > 30 THEN 'Good Day'
+    ELSE 'Bad Day'
+  END
+FROM orders;
+
+-- MySQL syntax
+SELECT weekday_nr,
+  CASE WHEN weekday_nr = 1 THEN 'Monday'
+    WHEN weekday_nr = 2 THEN 'Tuesday'
+    WHEN weekday_nr = 3 THEN 'Wednesday'
+    WHEN weekday_nr = 4 THEN 'Thursday'
+    WHEN weekday_nr = 5 THEN 'Friday'
+    WHEN weekday_nr = 6 THEN 'Saturday'
+    ELSE 'Sunday'
+  END
+FROM (
+  SELECT WEEKDAY(last_checkin) + 1 AS weekday_nr
+  FROM memberships
+) AS weekday_numbers;
diff --git a/data/create-data/01-create-database.sql b/data/create-data/01-create-database.sql
new file mode 100644
index 0000000..378eb9d
--- /dev/null
+++ b/data/create-data/01-create-database.sql
@@ -0,0 +1 @@
+CREATE DATABASE gym;
diff --git a/data/create-data/02-create-table.sql b/data/create-data/02-create-table.sql
new file mode 100644
index 0000000..a389487
--- /dev/null
+++ b/data/create-data/02-create-table.sql
@@ -0,0 +1,14 @@
+CREATE TABLE memberships (
+    id INT PRIMARY KEY AUTO_INCREMENT, -- MySQL syntax
+    -- id SERIAL PRIMARY KEY, --PostgreSQL syntax
+    membership_start DATE,
+    membership_end DATE,
+    last_checkin TIMESTAMP,
+    last_checkout TIMESTAMP,
+    consumption NUMERIC(5, 2),
+    first_name VARCHAR(200),
+    last_name VARCHAR(200),
+    price NUMERIC(5, 2),
+    billing_frequency INT,
+    gender VARCHAR(200)
+);
diff --git a/data/create-data/03-add-table-data.sql b/data/create-data/03-add-table-data.sql
new file mode 100644
index 0000000..724409d
--- /dev/null
+++ b/data/create-data/03-add-table-data.sql
@@ -0,0 +1,8 @@
+INSERT INTO memberships (
+  membership_start, membership_end, last_checkin, last_checkout,
+  consumption, first_name, last_name, price, billing_frequency, gender
+)
+VALUES
+  ('2021-10-01', NULL, '2021-10-01 05:17:36', '2021-10-01 06:20:45', 26.49, 'Max', 'Schwarz', 19.99, 12, 'male'),
+  ('2020-05-10', '2022-05-09', '2021-11-03 10:01:56', '2021-11-03 14:30:00', 100.26, 'Manu', 'Lorenz', 199.99, 1, 'male'),
+  ('2021-02-18', '2022-02-17', '2021-10-29 15:26:05', '2021-10-29 17:01:33', 5.10, 'Julie', 'Barnes', 199.99, 1, 'female');
diff --git a/data/create-data/04-create-additional-tables.sql b/data/create-data/04-create-additional-tables.sql
new file mode 100644
index 0000000..9d198f9
--- /dev/null
+++ b/data/create-data/04-create-additional-tables.sql
@@ -0,0 +1,14 @@
+CREATE TABLE customers(
+  id INT PRIMARY KEY AUTO_INCREMENT, -- MySQL syntax
+  -- id SERIAL PRIMARY KEY, --PostgreSQL syntax
+  first_name VARCHAR(200),
+  last_name VARCHAR(200),
+  email VARCHAR(200)
+);
+
+CREATE TABLE orders(
+  id INT PRIMARY KEY AUTO_INCREMENT, -- MySQL syntax
+  -- id SERIAL PRIMARY KEY, --PostgreSQL syntax
+  amount_billed NUMERIC(5, 2),
+  customer_id INT REFERENCES customers
+);
\ No newline at end of file
diff --git a/data/create-data/05-insert-additional-data.sql b/data/create-data/05-insert-additional-data.sql
new file mode 100644
index 0000000..7f8363e
--- /dev/null
+++ b/data/create-data/05-insert-additional-data.sql
@@ -0,0 +1,8 @@
+INSERT INTO customers(first_name, last_name, email)
+VALUES
+  ('Max', 'Schwarz', 'max@test.com'),
+  ('Manu', 'Lorenz', 'manu@test.com'),
+  ('Julia', 'Meyers', 'juli@test.com');
+
+INSERT INTO orders(amount_billed, customer_id)
+VALUES (48.99,1), (27.45, 2), (19.49, 1), (8.49, 3);
diff --git a/data/create-data/06-add-customer.sql b/data/create-data/06-add-customer.sql
new file mode 100644
index 0000000..b6a0e58
--- /dev/null
+++ b/data/create-data/06-add-customer.sql
@@ -0,0 +1,2 @@
+INSERT INTO customers(first_name, last_name, email)
+VALUES('Ken', 'Brooks', 'ken@test.com');