Assignment_two_SQL

02_activities/assignments/DC_Cohort/Assignment2.md

@@ -14,9 +14,9 @@
     * Open a private window in your browser. Copy and paste the link to your pull request into the address bar. Make sure you can see your pull request properly. This helps the technical facilitator and learning support staff review your submission easily.
 
 Checklist:
-- [ ] Create a branch called `assignment-two`.
-- [ ] Ensure that the repository is public.
-- [ ] Review [the PR description guidelines](https://github.com/UofT-DSI/onboarding/blob/main/onboarding_documents/submissions.md#guidelines-for-pull-request-descriptions) and adhere to them.
+- [X] Create a branch called `assignment-two`.
+- [ X] Ensure that the repository is public.
+- [ X] Review [the PR description guidelines](https://github.com/UofT-DSI/onboarding/blob/main/onboarding_documents/submissions.md#guidelines-for-pull-request-descriptions) and adhere to them.
 - [ ] Verify that the link is accessible in a private browser window.
 
 If you encounter any difficulties or have questions, please don't hesitate to reach out to our team via our Slack. Our Technical Facilitators and Learning Support staff are here to help you navigate any challenges.
@@ -55,7 +55,27 @@ The store wants to keep customer addresses. Propose two architectures for the CU
 
 ```
 Your answer...
-```
+`Overwrite is type 1, which changes overwrite the old values, so if the bookstore only ever needs the current address in the CUSTOMER_ADDRESS table, we will have these variables below: 
+
+  (customer_id, 
+  address_line1 ,
+  address_line2 ,
+  city,
+  state,
+  postal_code,
+  country)
+But if it can retain changes, it is gonna be type 2, meaning it keeps historical versions. So in the CUSTOMER_ADDRESS table, the below variables will exist: 
+(customer_id,
+  address_line1,
+  address_line2,
+  city,
+  state,
+  postal_code,
+  country,
+  effective_from,
+  effective_to,
+  effective_date,
+  changed_by) 
 
 ***
 
@@ -184,4 +204,4 @@ Consider, for example, concepts of labour, bias, LLM proliferation, moderating c
 
 ```
 Your thoughts...
-```
+The article suggests the myth: “The model did it” when in fact underpaid people did, because it suggested that many of the systems we treat as automated are underpinned by human work. The story implies that automated systems make those human workers invisible and may shift human labour behind the scenes. Which means their labour condition are unethical. From another point of view, there is a risk of human biases because those were humans who decided which data to include and which ones to exclude. As a result, humans inadvertently induce biases during their data collection for Neural nets or large language models. To remedy this, it is necessary to value the human labour in the process that we have vast access to computers, which can understand the dimensions of a hot dog! Use them with responsibility and also the vulnerability that makes these technologies possible.

02_activities/assignments/DC_Cohort/assignment_two.sql

@@ -0,0 +1,230 @@
+Write SQL
+COALESCE
+#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
+#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 column with nulls, 
+and 'unit' for the second column with nulls.
+
+SELECT
+  product_name
+  || ', '
+  || COALESCE(product_size, '')                -- first NULL -> blank
+  || ' ('
+  || COALESCE(product_qty_type, 'unit')        -- second NULL -> 'unit'
+  || ')' AS product_display
+FROM product;
+
+#Windowed Functions
+-- 1) build distinct visits per customer then number them
+WITH visits AS (
+  SELECT DISTINCT customer_id, market_date
+  FROM customer_purchases
+)
+SELECT
+  customer_id,
+  market_date,
+  ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY market_date) AS visit_number
+FROM visits
+ORDER BY customer_id, market_date;
+
+SELECT
+  customer_id,
+  market_date,
+  ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY market_date DESC) AS rn_desc
+FROM (
+  SELECT DISTINCT customer_id, market_date
+  FROM customer_purchases
+) AS distinct_visits
+ORDER BY customer_id, market_date DESC;
+
+WITH numbered_visits AS (
+  SELECT
+    customer_id,
+    market_date,
+    ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY market_date DESC) AS rn_desc
+  FROM (
+    SELECT DISTINCT customer_id, market_date
+    FROM customer_purchases
+  )
+)
+SELECT *
+FROM numbered_visits
+WHERE rn_desc = 1
+ORDER BY customer_id;
+
+
+#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.
+
+WITH distinct_customer_product_dates AS (
+  SELECT
+    customer_id,
+    product_id,
+    market_date
+  FROM customer_purchases
+  GROUP BY customer_id, product_id, market_date
+),
+
+
+counts AS (
+  SELECT
+    customer_id,
+    product_id,
+    COUNT(*) AS times_purchased_distinct_dates
+  FROM distinct_customer_product_dates
+  GROUP BY customer_id, product_id
+)
+
+
+SELECT
+  cp.*,
+  c.times_purchased_distinct_dates
+FROM customer_purchases cp
+LEFT JOIN counts c
+  ON cp.customer_id = c.customer_id
+  AND cp.product_id = c.product_id
+ORDER BY cp.customer_id, cp.product_id, cp.market_date;
+
+
+#String manipulations
+SELECT
+  product_name,
+  CASE
+    WHEN INSTR(product_name, '-') > 0 THEN
+      TRIM(SUBSTR(product_name, INSTR(product_name, '-') + 1))
+    ELSE
+      NULL
+  END AS description_after_hyphen
+FROM product
+WHERE INSTR(product_name, '-') > 0;  -- optionally filter only rows that have a hyphen
+
+#Filter the query to show any product_size value that contain a number with REGEXP.
+SELECT *
+FROM product
+WHERE product_size REGEXP '[0-9]';
+
+#UNION
+Using a UNION, write a query that displays the market dates with the highest and lowest total sales.
+
+WITH totals AS (
+  SELECT
+    market_date,
+    SUM(cost_to_customer_per_qty) AS total_sales
+  FROM customer_purchases
+  GROUP BY market_date
+),
+ranked AS (
+  SELECT
+    market_date,
+    total_sales,
+    RANK() OVER (ORDER BY total_sales DESC) AS rank_desc,   -- 1 = highest
+    RANK() OVER (ORDER BY total_sales ASC) AS rank_asc       -- 1 = lowest
+  FROM totals
+)
+-- pick highest total_sales days (rank_desc = 1) union lowest (rank_asc = 1)
+SELECT 'best_day' AS which, market_date, total_sales
+FROM ranked
+WHERE rank_desc = 1
+
+UNION
+
+SELECT 'worst_day' AS which, market_date, total_sales
+FROM ranked
+WHERE rank_asc = 1
+ORDER BY which;
+
+
+Section 3:
+
+#Cross Join
+
+WITH vp AS (
+  SELECT
+    v.vendor_id,
+    v.vendor_name,
+    p.product_id,
+    p.product_name,
+    v.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
+  GROUP BY v.vendor_id, v.vendor_name, p.product_id, p.product_name, v.original_price
+),
+cust AS (
+  SELECT customer_id FROM customer
+)
+-- Cross join vp with every customer and sum 5 * price for each cross row
+SELECT
+  vp.vendor_name,
+  vp.product_name,
+  SUM(5 * vp.original_price) AS projected_revenue     -- each cross-row contributes 5*price
+FROM vp
+CROSS JOIN cust
+GROUP BY vp.vendor_id, vp.product_id, vp.vendor_name, vp.product_name
+ORDER BY vp.vendor_name, vp.product_name;
+
+#INSERT
+Create a new table "product_units".
+DROP TABLE IF EXISTS product_units;
+
+CREATE TABLE product_units AS
+SELECT
+  p.*,
+  CURRENT_TIMESTAMP AS snapshot_timestamp
+FROM product p
+WHERE product_qty_type = 'unit';
+
+
+PRAGMA table_info(product_units);
+SELECT * FROM product_units LIMIT 10;
+
+#Using INSERT, add a new row to the product_unit 
+INSERT INTO product_units
+SELECT
+  p.*,
+  CURRENT_TIMESTAMP
+FROM product p
+WHERE p.product_name = 'Apple Pie'   -- change product name if needed
+LIMIT 1;
+
+#DELETE
+DELETE FROM product_units
+WHERE product_name = 'Apple Pie'
+  AND snapshot_timestamp < (
+    SELECT MAX(snapshot_timestamp)
+    FROM product_units pu2
+    WHERE pu2.product_name = product_units.product_name
+  );
+
+  #UPDATE
+  ALTER TABLE product_units
+ADD current_quantity INT;
+
+
+SELECT
+  product_id,
+  quantity,
+  market_date
+FROM vendor_inventory
+WHERE (product_id, market_date) IN (
+  SELECT product_id, MAX(market_date)
+  FROM vendor_inventory
+  GROUP BY product_id
+);
+UPDATE product_units
+SET current_quantity = COALESCE(
+  (
+    SELECT vi.quantity
+    FROM vendor_inventory vi
+    WHERE vi.product_id = product_units.product_id
+    ORDER BY vi.market_date DESC
+    LIMIT 1
+  ),
+  0
+);
+