Second semester Altschool examination submission

infra_setup/init.sql

@@ -1,60 +1,73 @@
-
 -- Create schema
 CREATE SCHEMA IF NOT EXISTS ALT_SCHOOL;
 
-
 -- create and populate tables
-create table if not exists ALT_SCHOOL.PRODUCTS
-(
-    id  serial primary key,
-    name varchar not null,
-    price numeric(10, 2) not null
-);
-
+create table
+    if not exists ALT_SCHOOL.PRODUCTS (
+        id serial primary key,
+        name varchar not null,
+        price numeric(10, 2) not null
+    );
 
 COPY ALT_SCHOOL.PRODUCTS (id, name, price)
-FROM '/data/products.csv' DELIMITER ',' CSV HEADER;
+FROM
+    '/data/products.csv' DELIMITER ',' CSV HEADER;
 
 -- setup customers table following the example above
-
--- TODO: Provide the DDL statment to create this table ALT_SCHOOL.CUSTOMERS
-
--- TODO: provide the command to copy the customers data in the /data folder into ALT_SCHOOL.CUSTOMERS
-
-
-
--- TODO: complete the table DDL statement
-create table if not exists ALT_SCHOOL.ORDERS
-(
-    order_id uuid not null primary key,
-    -- provide the other fields
-);
-
-
--- provide the command to copy orders data into POSTGRES
-
-
-create table if not exists ALT_SCHOOL.LINE_ITEMS
-(
-    line_item_id serial primary key,
-    -- provide the remaining fields
-);
-
-
--- provide the command to copy ALT_SCHOOL.LINE_ITEMS data into POSTGRES
-
-
--- setup the events table following the examle provided
-create table if not exists ALT_SCHOOL.EVENTS
-(
-    -- TODO: PROVIDE THE FIELDS
-);
-
--- TODO: provide the command to copy ALT_SCHOOL.EVENTS data into POSTGRES
-
-
-
-
-
-
-
+create table
+    if not exists ALT_SCHOOL.CUSTOMERS (
+        customer_id uuid primary key,
+        device_id uuid NOT NULL,
+        "location" varchar(255) NOT NULL,
+        currency varchar(10) NULL
+    );
+
+-- copy the customers data in the /data folder into ALT_SCHOOL.CUSTOMERS
+COPY ALT_SCHOOL.CUSTOMERS (customer_id, device_id, "location", currency)
+FROM
+    '/data/customers.csv' DELIMITER ',' CSV HEADER;
+
+create table
+    if not exists ALT_SCHOOL.ORDERS (
+        order_id uuid not null primary key,
+        customer_id uuid not null,
+        "status" varchar(50) not null,
+        checked_out_at timestamp not null
+    );
+
+-- copy orders data into POSTGRES
+COPY ALT_SCHOOL.ORDERS (order_id, customer_id, "status", checked_out_at)
+FROM
+    '/data/orders.csv' DELIMITER ',' CSV HEADER;
+
+create table
+    if not exists ALT_SCHOOL.LINE_ITEMS (
+        line_item_id serial primary key,
+        order_id uuid NOT NULL,
+        item_id int8 NOT NULL,
+        quantity int8 NOT NULL
+    );
+
+-- copy ALT_SCHOOL.LINE_ITEMS data into POSTGRES
+COPY ALT_SCHOOL.LINE_ITEMS (line_item_id, order_id, item_id, quantity)
+FROM
+    '/data/line_items.csv' DELIMITER ',' CSV HEADER;
+
+-- setup the events table
+create table
+    if not exists ALT_SCHOOL.EVENTS (
+        event_id serial primary key,
+        customer_id uuid NOT NULL,
+        event_data jsonb NOT NULL,
+        event_timestamp timestamp NOT NULL
+    );
+
+-- copy ALT_SCHOOL.EVENTS data into POSTGRES
+COPY ALT_SCHOOL.EVENTS (
+    event_id,
+    customer_id,
+    event_data,
+    event_timestamp
+)
+FROM
+    '/data/events.csv' DELIMITER ',' CSV HEADER;

questions/answers.sql

@@ -0,0 +1,239 @@
+-- Question 2a.1
+/*
+what is the most ordered item based on the number of times it appears in an order cart that checked out successfully?
+
+To get the most ordered item, created 2 CTEs, most_ordered_items and most_ordered_items_rank.
+1. most_ordered_items: in this CTE, only product that are successfully checked out are selected. It is also worth nothing that the sum of 'quantity' of each product is used to determine
+	the number of times it appears in an order cart that checked out successfully.
+2. most_ordered_items_rank: in this CTE, the rank() function is used to rank the products based on the number of times they appear in an order cart that checked out successfully.
+	The rank is done in descending order, finally, filter from this CTE where the row_rank is equal to 1.
+
+Note: Do not use order by and limit in the final query, as it will not work in the case of ties.
+
+ */
+
+with
+	most_ordered_items as (
+		select
+			id as product_id,
+			name as product_name,
+			sum(quantity) as num_times_in_successful_orders
+		from
+			alt_school.orders o
+			join alt_school.line_items li using (order_id)
+			join alt_school.products p on li.item_id = p.id
+		where
+			status = 'success'
+		group by
+			id,
+			name,
+			status
+	),
+	most_ordered_items_rank as (
+		select
+			*,
+			rank() over (
+				order by
+					num_times_in_successful_orders desc
+			) row_rank
+		from
+			most_ordered_items
+	)
+select
+	product_id,
+	product_name,
+	num_times_in_successful_orders
+from
+	most_ordered_items_rank
+where
+	row_rank = 1;
+
+-- Question 2a.2
+/*
+without considering currency, and without using the line_item table, find the top 5 spenders 
+
+To find the top 5 spenders, created 3 CTEs, order_quantity, spender, and spender_rank.
+1. order_quantity: in this CTE, only customers who successfully checked out are selected.
+2. spender: in this CTE, the total spend of each customer is calculated by multiplying the quantity of each product by the price of the product.
+3. spender_rank: in this CTE, the rank() function is used to rank the customers based on the total spend.
+	The rank is done in descending order, finally, filter from this CTE where the row_rank is less than or equal to 5.
+
+Note: Do not use order by and limit 5 in the final query, as it will not work in the case of ties.
+*/
+with
+	order_quantity as (
+		select
+			customer_id,
+			e.event_data ->> 'event_type' as event_type,
+			e.event_data ->> 'item_id' as item_id,
+			e.event_data ->> 'quantity' as quantity
+		from
+			alt_school.events e
+		where
+			customer_id in (
+				select distinct
+					customer_id
+				from
+					alt_school.events e
+				where
+					e.event_data ->> 'status' = 'success'
+			)
+			and e.event_data ->> 'event_type' not in ('checkout', 'visit')
+	),
+	spender as (
+		select
+			customer_id,
+			sum(cast(quantity as integer) * price) as total_spend
+		from
+			order_quantity o
+			join alt_school.products p on cast(o.item_id as integer) = p.id
+		where
+			quantity is not null
+		group by
+			customer_id
+	),
+	spender_rank as (
+		select
+			customer_id,
+			location,
+			total_spend,
+			rank() over (
+				order by
+					total_spend desc
+			) ROW_RANK
+		from
+			spender
+			join alt_school.customers using (customer_id)
+	)
+select
+	customer_id,
+	location,
+	total_spend
+from
+	spender_rank
+where
+	row_rank <= 5;
+
+
+-- Question 2b.1 
+/* 
+Determine the most common location (country) where successful checkouts occurred
+To get the most common location where successful checkouts occurred, created 2 CTEs, location_count and location_count_rank.
+1. location_count: in this CTE, only successful checkouts are selected. The count of successful checkouts is grouped by location.
+2. location_count_rank: in this CTE, the rank() function is used to rank the locations based on the number of successful checkouts.
+	The rank is done in descending order, finally, filter from this CTE where the row_rank is equal to 1.
+*/ 
+
+with
+	location_count as (
+		select
+			location,
+			count(1) as checkout_count
+		from
+			alt_school.events e
+			join alt_school.customers using (customer_id)
+		where
+			e.event_data ->> 'event_type' = 'checkout'
+			and e.event_data ->> 'status' = 'success'
+		group by
+			location
+	),
+	location_count_rank as (
+		select
+			location,
+			checkout_count,
+			rank() over (
+				order by
+					checkout_count desc
+			) row_rank
+		from
+			location_count
+	)
+select
+	location,
+	checkout_count
+from
+	location_count_rank
+where
+	row_rank = 1;
+
+
+-- Question 2b.2
+/* 
+Identify the customers who abandoned their carts and count the number of events (excluding visits) that occurred before the abandonment
+
+To identify the customers who abandoned their carts, created a CTE.
+1. event_group: in this CTE, the count of all events, grouped by customer_id, event_type, and status.
+2. In the final query, get the unique list  of customers (id) who successfully checked out (a subquery is used to get this list).
+	filter by the result of the subquery, by excluding customers who successfully checked out, the result will be customers who abandoned their carts.
+	In addition, exclude events of type 'visit' from customers who abandoned their carts. 
+	Sum the count of remaining events that occurred grouped by customer_id, this result to the num_of_events before the abandonment.
+
+*/
+with
+	event_group as (
+		select
+			customer_id,
+			e.event_data ->> 'event_type' as event_type,
+			e.event_data ->> 'status' as status,
+			count(1) as event_count
+		from
+			alt_school.events e
+		group by
+			customer_id,
+			e.event_data ->> 'event_type',
+			e.event_data ->> 'status'
+	)
+select
+	customer_id,
+	sum(event_count) as num_events
+from
+	event_group
+	join alt_school.customers c using (customer_id)
+where
+	customer_id not in (
+		select distinct
+			customer_id
+		from
+			event_group
+		where
+			event_type = 'checkout'
+			and status = 'success'
+	)
+	and event_type != 'visit'
+group by
+	customer_id;
+
+-- question 2b.3
+/*
+Find the average number of visits per customer, considering only customers who completed 
+
+To find the average number of visits per customer, created a CTE.
+1. event_group: in this CTE, the count distinct event of all event_data[timestamp] events, grouped by customer_id.
+	filter for customers who successfully checked out by using a subquery returns a list, and  considering only event_type is 'visit'.
+	In the final query, get the average of the event_count.
+*/
+with
+	event_group as (
+		select
+			customer_id,
+			count(distinct e.event_data ->> 'timestamp') as event_count
+		from
+			alt_school.events e
+		where
+			customer_id in (
+				select distinct
+					customer_id
+				from
+					alt_school.events e
+				where
+					e.event_data ->> 'status' = 'success'
+			)
+			and e.event_data ->> 'event_type' = 'visit'
+		group by
+			customer_id
+	)
+select
+	round(avg(event_count), 2) as average_visits
+from
+	event_group;