doc: How to code subqueries

How_to_code_subqueries.sql

@@ -0,0 +1,110 @@
+/*1*/
+SELECT 
+	DISTINCT category_name
+FROM 
+	categories c 
+WHERE 
+	category_id 
+	IN (select product_id FROM products)
+ORDER BY 
+	category_name
+LIMIT 3;
+
+/*2*/
+SELECT 
+	product_name,
+    list_price
+FROM 
+	products
+
+GROUP BY 
+	product_name 
+HAVING
+	AVG(list_price) > (SELECT AVG(list_price) FROM products)
+ORDER BY list_price DESC;
+
+/*3*/
+SELECT
+	category_name
+FROM 
+	categories c
+    WHERE NOT exists
+	(SELECT category_name, category_id 
+    FROM products p
+    WHERE c.category_id= p.category_id);
+
+/*4 part 1*/ /*kan het dat in bedrag anders is*/
+SELECT
+	email_address,
+    o.order_id,
+    SUM(item_price - discount_amount) * quantity AS 'order_total'
+FROM 
+    customers c
+JOIN 
+	orders o
+USING 
+	(customer_id)
+JOIN
+	order_items oi
+USING 
+	(order_id)
+GROUP BY
+	email_address,
+    o.order_id;
+    
+/*4 part 2*/ /*fout*/
+SELECT
+	email_address,
+    MAX(item_price)
+FROM
+	(SELECT
+	email_address,
+    o.order_id,
+    SUM(item_price - discount_amount) * quantity AS 'order_total'
+FROM 
+    customers c
+JOIN 
+	orders o
+USING 
+	(customer_id)
+JOIN
+	order_items oi
+USING 
+	(order_id)
+GROUP BY
+	email_address,
+    o.order_id) v
+    JOIN order_items
+    using (order_id);
+    
+/*5*/
+SELECT 
+	p1.product_name, 
+	p1.discount_percent
+FROM 
+	products p1
+WHERE 
+	p1.discount_percent NOT IN
+    (SELECT 
+		p2.discount_Percent
+     FROM 
+		Products p2
+     WHERE 
+		p1.product_name <> p2.product_name)
+ORDER BY product_name;
+
+/*6*/ /*fout*/
+SELECT
+	email_address,
+    order_id,
+    order_date
+FROM 
+	customers c
+JOIN 
+	orders o
+ON 
+	c.customer_id = o.customer_id
+WHERE 
+	(SELECT MIN(ord.order_date) FROM orders ord
+    JOIN customers c1 ON  ord.customer_id = c1.customer_id
+    GROUP BY c1.customer_id);

Solution Exercises.sql

@@ -36,12 +36,12 @@ SELECT
 	product_name,
     list_price,
     discount_percent,
-    ROUND((list_price*(discount_percent/100)),2) AS discount_amount,
-    ROUND(list_price +(list_price*(discount_percent/100)),2) AS discount_price
+    ROUND((list_price*discount_percent/100,2) AS discount_amount,
+    ROUND(list_price - list_price*discount_percent/100,2)AS discount_price
 FROM
 	products
 ORDER BY 
-	discount_price DESC
+	ROUND(list_price -(list_price*(discount_percent/100)),2 DESC
 LIMIT 5;
 
 /*5*/
@@ -208,6 +208,44 @@ WHERE
 ORDER BY
 	order_date;
     
+    
+/* HOW TO CODE SUMMARY QUERRIES*/
+
+/*1*/
+SELECT
+    count(*) AS count_number_of_orders,
+    SUM(tax_amount) AS sum_tax_amounts
+FROM
+	orders;
+
+/*2*/
+SELECT
+	category_name,
+	COUNT(*) AS count_of_the_products,
+    MAX(list_price)
+FROM 
+	products p
+JOIN
+	categories c
+ON
+	p.category_id = c.category_id
+GROUP BY 
+	category_name
+ORDER BY COUNT(*) DESC;
+
+/*3*/
+SELECT 
+	email_adress
+	
+    
+    
+    SELECT category_name FROM categories;
+    
+    
+
+
+
+    
 	
 
  
@@ -219,4 +257,3 @@ ORDER BY
 
 
     
-