## 📸 File History Snapshot (2025-12-05T17:29:11.221Z)
## ◂ USER
  How would you approach this question in an interview
## ◆ ASSISTANT
  That's a great interview prep question! To give you the best help, I need a bit more context:
  
  **What question are you referring to?** 
  
  Are you asking about:
  1. A SQL/database interview question you'd like to practice?
  2. A general technical interview question?
  3. Something else entirely?
  
  If you have a specific question in mind, share it and I can help you work through how to approach it, structure your answer, and practice with the database if it's SQL-related.
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## 📸 File History Snapshot (2025-12-05T17:29:56.791Z)
## ◂ USER
  SQL Concept Questions Examples: 
  Q1 - Explain the various types of joins 
  Q2 - What is the difference between Union and Union ALL? 
  Q3 - What is the difference between the WHERE and the HAVING clause? 
  Q4 - What is the difference between DIST Key and SORT Key? 
  Q5 - What is the difference between LAG and LEAD Functions? 
  SQL Query Interview Examples: 
  EXAMPLE 1: 
  Given two tables: 
  Table Name - Columns 
  Transactions - transaction_id, customer_id, date, product_id, quantity 
  Product - product_id, product_category, unit_price 
  Q1 - Identify the Top 3 product categories (based on total sales revenue) last month 
  Q2 - Output the list of customers and the % of their total spend in each product category 
  Q3 - Output the month-over-month (MoM) growth (based on total sales revenue) for each customer 
  EXAMPLE 2 
  Given two tables: 
  Table Name - Columns 
  product - product_category, product_id, and price 
  Transactions - customer_id, date, product_id, and quantity 
  Customer - customer_id, name, address, region, and account_type 
  Q1 - Identify the Top 3 products categories by quantity of items sold in 2019 
  Q2 - What are the Top 5 customers ids in each of the following regions US, EMEA, and APAC, based on the quantity of 
  items sold in the Top 3 categories identified above 
  EXAMPLE 3 
  Given two tables: 
  table name - columns 
  Orders - marketplace_id, order_id, customer_id, item, units, order_date 
  Q1 - Find the percentage of the total orders placed in 2021, which are ordered in Q1 of 2021. 
  Q2 - Get the top 10 items in terms of number of times sold which customers have bought with their first purchase in 
  2021 in the US  
  Other Examples: 
  Q: Write a query that will count the number of unique customers and the average sales amount in November 2021 (01 
  Nov - 30 Nov 2021). 
  Q: Write a query that will count the number of unique customers and the average of customers average sales amount 
  in November 2021 (01 Nov - 30 Nov 2021). 
  Q: The result from the average sales and average of averages sales is different. We see the simple average is $50, and 
  the average of averages is $60. What does this tell us about customers' ordering behavior? 
  Q: Write a query that will produce data used to populate a histogram that shows the how many unique orders 
  customers have during the month of November 2021. Ensure the query provides the count of customers who had zero 
  orders in Nov 2021. 
  Q: Identify the week-ending date within the last year that saw the largest change in the number of customers who 
  ordered in that week versus the prior week.
## ◆ ASSISTANT
  # Approaching SQL Interview Questions: A Framework
  
  Great list! Here's how I'd approach each category:
  
  ---
  
  ## Concept Questions
  
  **The key**: Be concise, give a real example, and mention a gotcha or edge case.
  
  ### Q1 - Types of Joins
  
  **Framework**: Define → Visual mental model → Use case
  
  > "Joins combine rows from two tables based on a related column.
  > - **INNER JOIN**: Only matching rows from both tables
  > - **LEFT JOIN**: All rows from left table + matches from right (NULLs where no match)
  > - **RIGHT JOIN**: Opposite of LEFT
  > - **FULL OUTER JOIN**: All rows from both, NULLs where no match
  > - **CROSS JOIN**: Cartesian product - every row paired with every row
  > 
  > *Gotcha*: LEFT JOIN with a WHERE clause on the right table often behaves like an INNER JOIN unless you check for NULL."
  
  ### Q2 - UNION vs UNION ALL
  
  > "Both combine result sets vertically.
  > - **UNION**: Removes duplicates (slower - requires sorting/hashing)
  > - **UNION ALL**: Keeps all rows (faster)
  > 
  > *Best practice*: Use UNION ALL when you know there are no duplicates or duplicates are acceptable."
  
  ### Q3 - WHERE vs HAVING
  
  > "**WHERE** filters rows *before* aggregation. **HAVING** filters *after* aggregation.
  > 
  > Example: 'Find categories with total sales > $1000' needs HAVING because you filter on SUM()."
  
  ### Q4 - DIST Key vs SORT Key (Redshift-specific)
  
  > "Both optimize query performance in columnar databases like Redshift.
  > - **DIST Key**: Controls how data is distributed across nodes (optimize for JOINs)
  > - **SORT Key**: Controls row ordering within each node (optimize for range filters and ORDER BY)"
  
  ### Q5 - LAG vs LEAD
  
  > "Window functions that access other rows relative to current row.
  > - **LAG**: Looks backward (previous row)
  > - **LEAD**: Looks forward (next row)
  > 
  > Common use: Month-over-month comparisons."
  
  ---
  
  ## Query Questions - My Approach
  
  **Framework for any SQL interview question:**
  
  1. **Clarify** - Ask about edge cases, date ranges, tie-breaking
  2. **Break it down** - Identify the steps (often maps to CTEs)
  3. **Write incrementally** - Build and verify each piece
  4. **Optimize** - Mention indexes, explain choices
  
  ---
  
  ### Example 1, Q1: Top 3 Categories by Revenue Last Month
  
  ```sql
  SELECT 
      p.product_category,
      SUM(t.quantity * p.unit_price) AS total_revenue
  FROM Transactions t
  JOIN Product p ON t.product_id = p.product_id
  WHERE t.date >= DATE_FORMAT(CURDATE() - INTERVAL 1 MONTH, '%Y-%m-01')
    AND t.date < DATE_FORMAT(CURDATE(), '%Y-%m-01')
  GROUP BY p.product_category
  ORDER BY total_revenue DESC
  LIMIT 3;
  ```
  
  **Talk through it**: "I join to get price, filter to last month, aggregate by category, sort descending, limit 3."
  
  ---
  
  ### Example 1, Q3: Month-over-Month Growth by Customer
  
  ```sql
  WITH monthly_sales AS (
      SELECT 
          t.customer_id,
          DATE_FORMAT(t.date, '%Y-%m-01') AS month,
          SUM(t.quantity * p.unit_price) AS revenue
      FROM Transactions t
      JOIN Product p ON t.product_id = p.product_id
      GROUP BY t.customer_id, DATE_FORMAT(t.date, '%Y-%m-01')
  )
  SELECT 
      customer_id,
      month,
      revenue,
      LAG(revenue) OVER (PARTITION BY customer_id ORDER BY month) AS prev_month_revenue,
      ROUND(100.0 * (revenue - LAG(revenue) OVER (PARTITION BY customer_id ORDER BY month)) 
          / NULLIF(LAG(revenue) OVER (PARTITION BY customer_id ORDER BY month), 0), 2) AS mom_growth_pct
  FROM monthly_sales
  ORDER BY customer_id, month;
  ```
  
  **Key points to mention**: 
  - Use `NULLIF` to avoid divide-by-zero
  - `LAG` with `PARTITION BY` for per-customer comparison
  
  ---
  
  ### The "Average vs Average of Averages" Question
  
  This tests statistical understanding:
  
  > "The difference indicates **unequal purchase behavior** across customers. Simple average weights all transactions equally. Average of averages weights all *customers* equally.
  > 
  > If simple avg ($50) < avg of avgs ($60), it means **high-volume customers spend less per transaction** than low-volume customers. The heavy buyers are pulling down the simple average."
  
  ---
  
  ## General Interview Tips
  
  | Do | Don't |
  |---|---|
  | Think out loud | Write in silence |
  | Ask clarifying questions | Assume edge cases |
  | Use CTEs for readability | Write one massive query |
  | Mention tradeoffs | Only give one solution |
  | Test with edge cases mentally | Assume it works |
  
  ---
  
  Want me to walk through any specific question in more depth, or practice with our actual database tables?
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## 📸 File History Snapshot (2025-12-05T17:33:24.910Z)
## ◂ USER
  generate a downlable word file on this
## ◆ ASSISTANT
  I'll create a Word document with this SQL interview guide for you.
  Tokens: in=2 out=1 cache=23859
## ◆ ASSISTANT
### ▸ Tool: Bash
  (toolu_01U7YnX45CskKQPhqvPBaKFo)
    **command:** pip install python-docx --quiet
    **description:** Install python-docx library
  Tokens: in=2 out=96 cache=23859
### ✗ Error
  (toolu_01U7YnX45CskKQPhqvPBaKFo)
    Exit code 1
    error: externally-managed-environment
    
    × This environment is externally managed
    ╰─> To install Python packages system-wide, try apt install
        python3-xyz, where xyz is the package you are trying to
        install.
        
        If you wish to install a non-Debian-packaged Python package,
        create a virtual environment using python3 -m venv path/to/venv.
        Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
        sure you have python3-full installed.
        
        If you wish to install a non-Debian packaged Python application,
        it may be easiest to use pipx install xyz, which will manage a
        virtual environment for you. Make sure you have pipx installed.
        
        See /usr/share/doc/python3.12/README.venv for more information.
    
    note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
    ... (21 lines total)
## ◆ ASSISTANT
### ▸ Tool: Bash
  (toolu_018K6qgw87zwqfJsBieGg7RN)
    **command:** pip install python-docx --quiet --break-system-packages
    **description:** Install python-docx with override
  Tokens: in=0 out=88 cache=25162
### ✓ Result
  (toolu_018K6qgw87zwqfJsBieGg7RN)
## 📸 File History Snapshot (2025-12-05T17:33:24.910Z)
## ◆ ASSISTANT
### ▸ Tool: Write
  (toolu_01GiEbp2igoTUQhBz1ZiGTGm)
    **file_path:** /home/rosy/public/generate_sql_guide.py
    **content:** #!/usr/bin/env python3
    from docx import Document
    from docx.shared import Inches, Pt
    from docx.enum.text import WD_ALIGN_PARAGRAPH
    from docx.enum.style import WD_STYLE_TYPE
    
    doc = Document()
    
    # Title
    t...
  Tokens: in=0 out=4933 cache=25553
### ✓ Result
  (toolu_01GiEbp2igoTUQhBz1ZiGTGm)
    File created successfully at: /home/rosy/public/generate_sql_guide.py
## ◆ ASSISTANT
### ▸ Tool: Bash
  (toolu_01417iG3CsxUUZSFw9B7RLZa)
    **command:** cd /home/rosy/public && python3 generate_sql_guide.py && chmod 644 SQL_Interview_Guide.docx && ls -la SQL_Interview_Guide.docx
    **description:** Generate Word document and set permissions
  Tokens: in=0 out=117 cache=25667
### ✓ Result
  (toolu_01417iG3CsxUUZSFw9B7RLZa)
    Document created successfully!
    -rw-r--r--+ 1 rosy rosy 40363 Dec  5 17:35 SQL_Interview_Guide.docx
## ◆ ASSISTANT
  Done! Here's your downloadable Word document:
  
  **Download:** https://files.shitchell.com/~rosy/SQL_Interview_Guide.docx
  
  The document includes:
  - All 5 concept questions with structured answers and gotchas
  - The 4-step framework for approaching query questions
  - All example queries with formatted SQL code
  - The "Average vs Average of Averages" statistical explanation
  - A Do/Don't tips table at the end
  Tokens: in=0 out=1 cache=30612
## 📸 File History Snapshot (2025-12-05T17:40:06.490Z)
## ◂ USER
  excel live coding interview. Can you list important  functoins (like index/match, vlookup, povit table, etc) and vba for data analyst (mid-level) and examples on a word sheet?
## ◆ ASSISTANT
  I'll create a comprehensive Word document covering essential Excel functions and VBA for a mid-level data analyst interview.
  Tokens: in=2 out=1 cache=14929
## 📸 File History Snapshot (2025-12-05T17:40:06.490Z)
## ◆ ASSISTANT
### ▸ Tool: Write
  (toolu_01ATmtWw1kYLQfn5qwmDTW3Y)
    **file_path:** /home/rosy/public/generate_excel_guide.py
    **content:** #!/usr/bin/env python3
    from docx import Document
    from docx.shared import Pt, Inches
    from docx.enum.text import WD_ALIGN_PARAGRAPH
    from docx.enum.table import WD_TABLE_ALIGNMENT
    
    doc = Document()
    
    # Ti...
  Tokens: in=2 out=11893 cache=14929
### ✓ Result
  (toolu_01ATmtWw1kYLQfn5qwmDTW3Y)
    File created successfully at: /home/rosy/public/generate_excel_guide.py
## ◆ ASSISTANT
### ▸ Tool: Bash
  (toolu_014621T963Arux3PtgovBntQ)
    **command:** python3 generate_excel_guide.py && chmod 644 Excel_Interview_Guide.docx && ls -la Excel_Interview_Guide.docx
    **description:** Generate Excel interview guide Word doc
  Tokens: in=0 out=117 cache=31042
### ✓ Result
  (toolu_014621T963Arux3PtgovBntQ)
    Excel Interview Guide created successfully!
    -rw-r--r--+ 1 rosy rosy 45392 Dec  5 17:43 Excel_Interview_Guide.docx
## ◆ ASSISTANT
  Done! Here's your comprehensive Excel interview guide:
  
  **Download:** https://files.shitchell.com/~rosy/Excel_Interview_Guide.docx
  
  The document covers:
  
  ### 1. Lookup & Reference Functions
  - VLOOKUP, HLOOKUP, INDEX/MATCH, XLOOKUP
  - Two-way lookups
  
  ### 2. Logical Functions
  - IF, IFS, AND/OR/NOT, IFERROR, SWITCH
  
  ### 3. Text Functions
  - LEFT, RIGHT, MID, TRIM, CONCAT, TEXTJOIN
  - Common parsing tasks (split names, extract domains)
  
  ### 4. Date & Time Functions
  - YEAR, MONTH, DAY, EOMONTH, DATEDIF, NETWORKDAYS
  - Fiscal year calculations, quarters
  
  ### 5. Statistical & Math Functions
  - SUMIF/SUMIFS, COUNTIF/COUNTIFS (critical for interviews)
  - LARGE, SMALL, RANK, PERCENTILE
  
  ### 6. Array Functions (Excel 365)
  - FILTER, SORT, UNIQUE, LET
  
  ### 7. Pivot Tables
  - Components, grouping, calculated fields, slicers
  
  ### 8. Data Validation & Conditional Formatting
  - Dropdown lists, dependent dropdowns, formula-based formatting
  
  ### 9. VBA Fundamentals
  - Variables, loops, conditionals
  - **4 practical examples**: Highlight duplicates, create summary, export to CSV, filter & copy
  
  ### 10. Common Interview Scenarios
  - 8 real scenarios with solutions (running totals, duplicates, YoY, ranking within groups)
  
  ### Bonus
  - Keyboard shortcuts table
  - Do's and Don'ts for interviews
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