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Homework 4&5&6 #2

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Update homework_4.sql
movcha May 30, 2024
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Update homework_5.sql
movcha May 30, 2024
55e8f71
Update homework_6.md
movcha May 30, 2024
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150 changes: 129 additions & 21 deletions 03_homework/homework_4.sql
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-- COALESCE
/* 1. Our favourite manager wants a detailed long list of products, but is afraid of tables!
We tell them, no problem! We can produce a list with all of the appropriate details.
/*
1. Our favourite manager wants a detailed long list of products, but is afraid of tables!
We tell them, no problem! We can produce a list with all of the appropriate details.

Using the following syntax you create our super cool and not at all needy manager a list:

SELECT
product_name || ', ' || product_size|| ' (' || product_qty_type || ')'
FROM product
COALESCE(product_name, '') || ', ' ||
COALESCE(product_size, '') || ' (' ||
COALESCE(product_qty_type, 'unit') || ')'
FROM product;

But wait! The product table has some bad data (a few NULL values).
Find the NULLs and then using COALESCE, replace the NULL with a
blank for the first problem, and 'unit' for the second problem.
But wait! The product table has some bad data (a few NULL values).
Find the NULLs and then using COALESCE, replace the NULL with a
blank for the first problem, and 'unit' for the second problem.

HINT: keep the syntax the same, but edited the correct components with the string.
The `||` values concatenate the columns into strings.
Edit the appropriate columns -- you're making two edits -- and the NULL rows will be fixed.
All the other rows will remain the same.) */
HINT: keep the syntax the same, but edited the correct components with the string.
The `||` values concatenate the columns into strings.
Edit the appropriate columns -- you're making two edits -- and the NULL rows will be fixed.
All the other rows will remain the same.
*/




--Windowed Functions
/* 1. Write a query that selects from the customer_purchases table and numbers each customer’s
-- Windowed Functions
/*
1. Write a query that selects from the customer_purchases table and numbers each customer’s
visits to the farmer’s market (labeling each market date with a different number).
Each customer’s first visit is labeled 1, second visit is labeled 2, etc.

You can either display all rows in the customer_purchases table, with the counter changing on
each new market date for each customer, or select only the unique market dates per customer
(without purchase details) and number those visits.
HINT: One of these approaches uses ROW_NUMBER() and one uses DENSE_RANK(). */
HINT: One of these approaches uses ROW_NUMBER() and one uses DENSE_RANK().
*/

SELECT
customer_id,
market_date,
ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY market_date) as visit_number
FROM
customer_purchases;

/* 2. Reverse the numbering of the query from a part so each customer’s most recent visit is labeled 1,
/*
2. Reverse the numbering of the query from a part so each customer’s most recent visit is labeled 1,
then write another query that uses this one as a subquery (or temp table) and filters the results to
only the customer’s most recent visit. */
only the customer’s most recent visit.
*/

WITH reversed_visits AS (
SELECT
customer_id,
market_date,
ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY market_date DESC) as visit_number
FROM
customer_purchases
)
SELECT
customer_id,
market_date
FROM
reversed_visits
WHERE
visit_number = 1;

/*
3. Using a COUNT() window function, include a value along with each row of the
customer_purchases table that indicates how many different times that customer has purchased that product_id.
*/

SELECT
customer_id,
product_id,
quantity,
COUNT(*) OVER (PARTITION BY customer_id, product_id) as purchase_count
FROM
customer_purchases;

-- String manipulations
/*
1. Some product names in the product table have descriptions like "Jar" or "Organic".
These are separated from the product name with a hyphen.
Create a column using SUBSTR (and a couple of other commands) that captures these, but is otherwise NULL.
Remove any trailing or leading whitespaces. Don't just use a case statement for each product!

| product_name | description |
|----------------------------|-------------|
| Habanero Peppers - Organic | Organic |

/* 3. Using a COUNT() window function, include a value along with each row of the
customer_purchases table that indicates how many different times that customer has purchased that product_id. */
Hint: you might need to use INSTR(product_name,'-') to find the hyphens. INSTR will help split the column.
*/

SELECT
product_name,
TRIM(SUBSTR(product_name, INSTR(product_name, '-') + 2)) as description
FROM
product
WHERE
INSTR(product_name, '-') > 0;

-- UNION
/*
1. Using a UNION, write a query that displays the market dates with the highest and lowest total sales.

HINT: There are a possibly a few ways to do this query, but if you're struggling, try the following:
1) Create a CTE/Temp Table to find sales values grouped dates;
2) Create another CTE/Temp table with a rank windowed function on the previous query to create
"best day" and "worst day";
3) Query the second temp table twice, once for the best day, once for the worst day,
with a UNION binding them.
*/

WITH sales_summary AS (
SELECT
market_date,
SUM(quantity * cost_to_customer_per_qty) as total_sales
FROM
customer_purchases
GROUP BY
market_date
),
ranked_sales AS (
SELECT
market_date,
total_sales,
RANK() OVER (ORDER BY total_sales DESC) as sales_rank_desc,
RANK() OVER (ORDER BY total_sales ASC) as sales_rank_asc
FROM
sales_summary
)
SELECT
market_date,
total_sales,
'Highest Sales' as sales_type
FROM
ranked_sales
WHERE
sales_rank_desc = 1

UNION

SELECT
market_date,
total_sales,
'Lowest Sales' as sales_type
FROM
ranked_sales
WHERE
sales_rank_asc = 1;
113 changes: 55 additions & 58 deletions 03_homework/homework_5.sql
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-- String manipulations
/* 1. Some product names in the product table have descriptions like "Jar" or "Organic".
These are separated from the product name with a hyphen.
Create a column using SUBSTR (and a couple of other commands) that captures these, but is otherwise NULL.
Remove any trailing or leading whitespaces. Don't just use a case statement for each product!

| product_name | description |
|----------------------------|-------------|
| Habanero Peppers - Organic | Organic |

Hint: you might need to use INSTR(product_name,'-') to find the hyphens. INSTR will help split the column. */



/* 2. Filter the query to show any product_size value that contain a number with REGEXP. */



-- UNION
/* 1. Using a UNION, write a query that displays the market dates with the highest and lowest total sales.

HINT: There are a possibly a few ways to do this query, but if you're struggling, try the following:
1) Create a CTE/Temp Table to find sales values grouped dates;
2) Create another CTE/Temp table with a rank windowed function on the previous query to create
"best day" and "worst day";
3) Query the second temp table twice, once for the best day, once for the worst day,
with a UNION binding them. */



-- Cross Join
/*1. Suppose every vendor in the `vendor_inventory` table had 5 of each of their products to sell to **every**
customer on record. How much money would each vendor make per product?
Show this by vendor_name and product name, rather than using the IDs.
/* 1. Suppose every vendor in the `vendor_inventory` table had 5 of each of their products to sell to every customer on record.
How much money would each vendor make per product? Show this by vendor_name and product_name, rather than using the IDs.

HINT: Be sure you select only relevant columns and rows.
Remember, CROSS JOIN will explode your table rows, so CROSS JOIN should likely be a subquery.
Think a bit about the row counts: how many distinct vendors, product names are there (x)?
How many customers are there (y).
HINT: Be sure you select only relevant columns and rows. Remember, CROSS JOIN will explode your table rows, so CROSS JOIN should likely be a subquery.
Think a bit about the row counts: how many distinct vendors, product names are there (x)? How many customers are there (y).
Before your final group by you should have the product of those two queries (x*y). */


WITH vendor_product AS (
SELECT
v.vendor_name,
p.product_name,
vi.original_price
FROM vendor_inventory vi
JOIN vendor v ON vi.vendor_id = v.vendor_id
JOIN product p ON vi.product_id = p.product_id
),
customer_count AS (
SELECT COUNT(DISTINCT customer_id) AS num_customers FROM customer
)
SELECT
vp.vendor_name,
vp.product_name,
vp.original_price * 5 * cc.num_customers AS total_revenue
FROM vendor_product vp
CROSS JOIN customer_count cc
ORDER BY vp.vendor_name, vp.product_name;

-- INSERT
/*1. Create a new table "product_units".
This table will contain only products where the `product_qty_type = 'unit'`.
It should use all of the columns from the product table, as well as a new column for the `CURRENT_TIMESTAMP`.
/* 1. Create a new table "product_units". This table will contain only products where the `product_qty_type = 'unit'`.
It should use all of the columns from the product table, as well as a new column for the `CURRENT_TIMESTAMP`.
Name the timestamp column `snapshot_timestamp`. */



/*2. Using `INSERT`, add a new row to the product_units table (with an updated timestamp).
CREATE TABLE product_units AS
SELECT
product_id,
product_name,
product_size,
product_category_id,
product_qty_type,
CURRENT_TIMESTAMP AS snapshot_timestamp
FROM product
WHERE product_qty_type = 'unit';

/* 2. Using `INSERT`, add a new row to the product_units table (with an updated timestamp).
This can be any product you desire (e.g. add another record for Apple Pie). */


INSERT INTO product_units (product_id, product_name, product_size, product_category_id, product_qty_type, snapshot_timestamp)
VALUES (999, 'Cherry Pie', 'Large', 2, 'unit', CURRENT_TIMESTAMP);

-- DELETE
/* 1. Delete the older record for the whatever product you added.

HINT: If you don't specify a WHERE clause, you are going to have a bad time.*/


DELETE FROM product_units
WHERE product_id = 999
AND snapshot_timestamp < (SELECT MAX(snapshot_timestamp) FROM product_units WHERE product_id = 999);

-- UPDATE
/* 1.We want to add the current_quantity to the product_units table.
First, add a new column, current_quantity to the table using the following syntax.
/* 1. We want to add the current_quantity to the product_units table. First, add a new column, current_quantity to the table using the following syntax.

ALTER TABLE product_units
ADD current_quantity INT;

Then, using UPDATE, change the current_quantity equal to the last quantity value from the vendor_inventory details.

HINT: This one is pretty hard.
First, determine how to get the "last" quantity per product.
Second, coalesce null values to 0 (if you don't have null values, figure out how to rearrange your query so you do.)
Third, SET current_quantity = (...your select statement...), remembering that WHERE can only accommodate one column.
Finally, make sure you have a WHERE statement to update the right row,
you'll need to use product_units.product_id to refer to the correct row within the product_units table.
When you have all of these components, you can run the update statement. */
HINT: This one is pretty hard. First, determine how to get the "last" quantity per product. Second, coalesce null values to 0 (if you don't have null values, figure out how to rearrange your query so you do.)
Third, SET current_quantity = (...your select statement...), remembering that WHERE can only accommodate one column. Finally, make sure you have a WHERE statement to update the right row, you'll need to use product_units.product_id to refer to the correct row within the product_units table. When you have all of these components, you can run the update statement. */

ALTER TABLE product_units
ADD current_quantity INT;

UPDATE product_units
SET current_quantity = COALESCE((
SELECT quantity
FROM vendor_inventory vi
WHERE vi.product_id = product_units.product_id
ORDER BY vi.market_date DESC
LIMIT 1
), 0);
8 changes: 8 additions & 0 deletions 03_homework/homework_6.md
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<br>

**Write**: Reflect on your previous work and how you would adjust to include ethics and inequity components. Total length should be a few paragraphs, no more than one page.

Reflecting on previous tasks, I recognize the importance of incorporating ethics and equity to create fair, transparent, and responsible data systems. When creating logical data models or writing SQL queries, it’s crucial to protect personal information and consider measures like data anonymization.

Ensuring data privacy and security is a major ethical aspect. When working with sensitive information, such as customer data in farmersmarket.db, I must implement measures to protect it from unauthorized access. Additionally, maintaining data accuracy and integrity through regular audits is essential for making informed decisions.

The power of SQL in merging and summarizing data, particularly with JOIN and AGGREGATE functions, comes with the responsibility to prevent biases. For instance, when generating customer lists, it's vital to ensure the selection criteria do not discriminate against any group.

Moving forward, I will prioritize these principles to contribute to more ethical and equitable data practices.