for creation of tables, schema
it's simple

FOr insert query use MIgration script.
=============

🕵️‍♂️ SQL Detective Work - Mastering Data Investigation

📚 Essential Books (In Learning Order)

Level 1: SQL Investigation Fundamentals

"SQL Performance Explained" by Markus Winand 📖
- How to read execution plans
- Understanding what queries actually do
- Why: Helps you understand data patterns
"Learning SQL" by Alan Beaulieu
- Advanced GROUP BY, HAVING, window functions
- Why: These are your detective tools

Level 2: Data Analysis & Detective Skills

"Storytelling with Data" by Cole Nussbaumer Knaflic 📊
- How to ask the right questions
- Finding patterns in data
- Why: Teaches you HOW to think about data
"The Art of SQL" by Stéphane Faroult
- Advanced SQL patterns
- Performance investigation techniques
- Why: Shows you advanced detective queries

Level 3: System Analysis & Architecture

"Database Internals" by Alex Petrov
- How databases actually work
- Why: Understanding internals helps you ask better questions
"Designing Data-Intensive Applications" by Martin Kleppmann
- How systems are architected
- Why: Helps you understand WHY data is structured certain ways

🔧 Core Detective Techniques

1. The "Data Fingerprinting" Method


sql
-- Always start with basic profiling
SELECT 
    COUNT(*) as total_rows,
    COUNT(DISTINCT column1) as unique_col1,
    MIN(date_column) as earliest_date,
    MAX(date_column) as latest_date,
    COUNT(*) - COUNT(column2) as null_count_col2
FROM mysterious_table;

2. The "Relationship Hunter" Pattern


sql
-- Find unexpected relationships
SELECT 
    foreign_key,
    COUNT(DISTINCT related_field) as variety_count
FROM table1
GROUP BY foreign_key
HAVING COUNT(DISTINCT related_field) > 1  -- Red flag!
ORDER BY variety_count DESC;

3. The "Time Pattern Detective"


sql
-- Look for temporal patterns
SELECT 
    DATEPART(HOUR, timestamp_col) as hour_of_day,
    DATENAME(WEEKDAY, timestamp_col) as day_of_week,
    COUNT(*) as event_count
FROM events_table
GROUP BY DATEPART(HOUR, timestamp_col), DATENAME(WEEKDAY, timestamp_col)
ORDER BY event_count DESC;

4. The "Outlier Spotter"


sql
-- Find anomalies
WITH stats AS (
    SELECT 
        AVG(CAST(numeric_column AS FLOAT)) as avg_val,
        STDEV(CAST(numeric_column AS FLOAT)) as std_val
    FROM data_table
)
SELECT *
FROM data_table, stats
WHERE ABS(numeric_column - avg_val) > (3 * std_val);  -- 3 sigma rule

🎯 Mental Framework: "The 5 Whys of Data"

When you see surprising data, ask:

WHY does this pattern exist? (Business logic)
WHY is the data structured this way? (Technical architecture)
WHY are there exceptions? (Edge cases, legacy systems)
WHY now? (Temporal patterns, system changes)
WHY these specific values? (Domain knowledge, constraints)

🔍 Your Detective Skillset Development Plan

Week 1-2: Pattern Recognition

Practice with GROUP BY + HAVING combinations
Look for cardinality relationships (1:1, 1:many, many:many)
Master COUNT(DISTINCT) analysis

Week 3-4: Temporal Analysis

Date/time pattern queries
Trend analysis with window functions
Before/after comparisons

Week 5-6: Data Quality Investigation

NULL pattern analysis
Constraint violation detection
Referential integrity checks

Week 7-8: Performance Detective Work

Execution plan reading
Index usage analysis
Query optimization

🛠️ Essential SQL Tools for Detectives

Window Functions (Your Swiss Army Knife)


sql
-- Find duplicates and their patterns
SELECT *,
    ROW_NUMBER() OVER (PARTITION BY key_field ORDER BY date_field) as occurrence_number
FROM data_table
WHERE occurrence_number > 1;

CTEs for Complex Investigation


sql
WITH suspicious_patterns AS (
    SELECT field1, COUNT(*) as frequency
    FROM table1 
    GROUP BY field1
    HAVING COUNT(*) > (SELECT AVG(cnt) * 3 FROM (...))
)
SELECT * FROM table1 
WHERE field1 IN (SELECT field1 FROM suspicious_patterns);

CASE Statements for Categorization


sql
SELECT 
    CASE 
        WHEN pattern_field LIKE '%admin%' THEN 'System Account'
        WHEN pattern_field LIKE '%@%.%' THEN 'User Email'
        ELSE 'Unknown Pattern'
    END as account_type,
    COUNT(*)
FROM accounts
GROUP BY account_type;

🎓 Practice Exercises

Exercise 1: Mystery Database

Find a public dataset (like Northwind, Sakila) and:

Identify all tables and relationships
Find the "busiest" foreign keys
Spot data quality issues
Discover business rules from the data

Exercise 2: Performance Detective

Create a slow query
Use execution plans to find bottlenecks
Add indexes and measure improvement
Explain WHY it got faster

Exercise 3: Pattern Detective

Take any transaction table
Find temporal patterns (peak hours, seasonal trends)
Identify outliers and exceptions
Formulate hypotheses about business operations

🚀 Advanced Skills to Develop

1. Business Domain Knowledge

Learn the industry you're working in
Understand business processes
Why: Context helps you ask better questions

2. Statistics Fundamentals

Basic statistics (mean, median, standard deviation)
Correlation vs causation
Why: Helps you interpret what patterns mean

3. System Architecture Understanding

How databases are designed
ETL processes
Microservices data flow
Why: Helps you understand WHY data looks the way it does

💡 The Secret Sauce

What made your detective work brilliant:

You questioned assumptions (my denormalization theory)
You thought about business logic (call queues make sense)
You proposed testable hypotheses
You insisted on evidence (let's test with queries)

This is exactly how senior data professionals think!

🎯 Next Steps for You

Start with "SQL Performance Explained" - it's perfect for your level
Practice on your current database - you have real, complex data
Question everything - why are there 1,086 ExtNo values for DeviceId 0?
Document your findings - build a knowledge base of your discoveries

You already have the detective mindset - now you just need to build the technical toolkit! 🕵️‍♂️

📚 More Honest Book Recommendations:

For Actual SQL Detective Techniques:

"SQL Antipatterns" by Bill Karwin - Shows you what to look for when things go wrong
"SQL Performance Explained" by Markus Winand - How to investigate performance issues
"The Art of SQL" by Stéphane Faroult - Advanced investigation patterns

For Data Analysis Thinking:

"Thinking, Fast and Slow" by Daniel Kahneman - How to avoid bias in analysis
"The Signal and the Noise" by Nate Silver - Finding patterns vs noise
------------------------------

🕵️‍♂️ 20-Minute Daily SQL Detective Roadmap

Total Duration: 12 weeks (20 minutes/day, 5 days/week)
Goal: Transform from curious developer to SQL detective expert

📅 Week 1-2: Foundation Building

"Learn to Ask the Right Questions"

Daily 20-Minute Sessions:

Monday: Basic Data Profiling


sql
-- Template for every new table you encounter
SELECT 
    COUNT(*) as total_rows,
    COUNT(DISTINCT key_column) as unique_keys,
    MIN(date_column) as earliest_date,
    MAX(date_column) as latest_date
FROM your_table;

Practice: Apply to 1 table in your call center DB

Tuesday: Relationship Discovery


sql
-- Find surprising relationships
SELECT 
    foreign_key_column,
    COUNT(DISTINCT other_column) as variety_count
FROM your_table
GROUP BY foreign_key_column
HAVING COUNT(DISTINCT other_column) > 1
ORDER BY variety_count DESC;

Practice: Test different column combinations

Wednesday: NULL Pattern Analysis


sql
-- Find data quality issues
SELECT 
    'column_name' as field,
    COUNT(*) - COUNT(column_name) as null_count,
    (COUNT(*) - COUNT(column_name)) * 100.0 / COUNT(*) as null_percentage
FROM your_table;

Practice: Check all columns in one table

Thursday: DISTINCT Value Hunting


sql
-- Understand data variety
SELECT 
    column_name,
    COUNT(*) as frequency
FROM your_table
GROUP BY column_name
ORDER BY frequency DESC;

Practice: Find enum-like columns

Friday: Weekly Review + Documentation

Document 3 surprising discoveries
Note questions for next week
Review your detective notes

📖 Reading (5 min/day):

"SQL Performance Explained" - Chapter 1 & 2
Focus: Understanding what queries actually do

📅 Week 3-4: Time Detective

"Master Temporal Patterns"

Daily Sessions:

Monday: Hourly Patterns


sql
SELECT 
    DATEPART(HOUR, datetime_column) as hour_of_day,
    COUNT(*) as event_count
FROM your_table
GROUP BY DATEPART(HOUR, datetime_column)
ORDER BY hour_of_day;

Tuesday: Daily Patterns


sql
SELECT 
    DATENAME(WEEKDAY, datetime_column) as day_name,
    COUNT(*) as daily_count
FROM your_table
GROUP BY DATENAME(WEEKDAY, datetime_column)
ORDER BY daily_count DESC;

Wednesday: Monthly Trends


sql
SELECT 
    YEAR(datetime_column) as year,
    MONTH(datetime_column) as month,
    COUNT(*) as monthly_count
FROM your_table
GROUP BY YEAR(datetime_column), MONTH(datetime_column)
ORDER BY year, month;

Thursday: Peak Detection


sql
-- Find your busiest times
WITH hourly_stats AS (
    SELECT 
        DATEPART(HOUR, datetime_column) as hour,
        COUNT(*) as cnt
    FROM your_table
    GROUP BY DATEPART(HOUR, datetime_column)
)
SELECT * FROM hourly_stats
WHERE cnt > (SELECT AVG(cnt) * 1.5 FROM hourly_stats);

Friday: Document Patterns

What are your peak hours?
Any surprising temporal patterns?
Business explanations for patterns?

📖 Reading:

"SQL Performance Explained" - Chapter 3 & 4

📅 Week 5-6: Advanced Relationships

"Become a Relationship Expert"

Daily Sessions:

Monday: One-to-Many Detection


sql
-- Find 1:many relationships
SELECT 
    parent_id,
    COUNT(*) as child_count
FROM child_table
GROUP BY parent_id
HAVING COUNT(*) > 1
ORDER BY child_count DESC;

Tuesday: Many-to-Many Discovery


sql
-- Junction table analysis
SELECT 
    'Forward' as direction,
    first_id,
    COUNT(DISTINCT second_id) as related_count
FROM junction_table
GROUP BY first_id
HAVING COUNT(DISTINCT second_id) > 1
UNION ALL
SELECT 
    'Reverse' as direction,
    second_id,
    COUNT(DISTINCT first_id) as related_count
FROM junction_table
GROUP BY second_id
HAVING COUNT(DISTINCT first_id) > 1;

Wednesday: Orphan Detection


sql
-- Find orphaned records
SELECT 'Orphans in child table' as issue, COUNT(*)
FROM child_table c
LEFT JOIN parent_table p ON c.parent_id = p.id
WHERE p.id IS NULL;

Thursday: Referential Integrity Check


sql
-- Check data consistency
SELECT 
    'Missing references' as issue,
    COUNT(*) as count
FROM table_a a
LEFT JOIN table_b b ON a.foreign_key = b.primary_key
WHERE b.primary_key IS NULL AND a.foreign_key IS NOT NULL;

Friday: Relationship Mapping

Draw a simple diagram of table relationships
Document any weird relationships you found

📖 Reading:

"The Art of SQL" - Chapters 1-3

📅 Week 7-8: Outlier Detective

"Find the Unusual and Unexpected"

Daily Sessions:

Monday: Statistical Outliers


sql
-- Find extreme values
WITH stats AS (
    SELECT 
        AVG(CAST(numeric_column AS FLOAT)) as mean_val,
        STDEV(CAST(numeric_column AS FLOAT)) as std_val
    FROM your_table
)
SELECT *
FROM your_table, stats
WHERE ABS(numeric_column - mean_val) > (2 * std_val);

Tuesday: Frequency Outliers


sql
-- Find unusual patterns
WITH freq_analysis AS (
    SELECT 
        category_column,
        COUNT(*) as frequency,
        AVG(COUNT(*)) OVER() as avg_frequency
    FROM your_table
    GROUP BY category_column
)
SELECT *
FROM freq_analysis
WHERE frequency < avg_frequency * 0.1  -- Less than 10% of average
   OR frequency > avg_frequency * 3;    -- More than 3x average

Wednesday: Length Outliers


sql
-- Find unusual text lengths
SELECT 
    column_name,
    LEN(column_name) as text_length,
    *
FROM your_table
WHERE LEN(column_name) > (
    SELECT AVG(LEN(column_name)) + 2 * STDEV(LEN(column_name))
    FROM your_table
)
ORDER BY text_length DESC;

Thursday: Date Outliers


sql
-- Find unusual dates
SELECT *
FROM your_table
WHERE date_column < '2020-01-01'  -- Too old?
   OR date_column > GETDATE()     -- Future dates?
   OR YEAR(date_column) = 1900;   -- Default dates?

Friday: Document Anomalies

List all outliers found
Hypothesize why they exist
Plan investigation for next week

📖 Reading:

"SQL Antipatterns" - Chapters 1-4

📅 Week 9-10: Performance Detective

"Understand What Makes Queries Slow"

Daily Sessions:

Monday: Execution Plan Basics


sql
-- Turn on execution plans
SET SHOWPLAN_ALL ON;
-- Run a simple query and study the plan
SELECT * FROM your_large_table WHERE some_column = 'value';
SET SHOWPLAN_ALL OFF;

Tuesday: Index Usage Analysis


sql
-- Find missing indexes
SELECT 
    column_name,
    COUNT(*) as usage_frequency
FROM your_table
WHERE column_name = 'frequently_searched_value'
GROUP BY column_name;
-- Check if this column has an index

Wednesday: Slow Query Hunting


sql
-- Find potentially slow patterns
SELECT COUNT(*)
FROM large_table l1
JOIN another_large_table l2 ON l1.unindexed_column = l2.unindexed_column;
-- Time this query!

Thursday: Data Distribution Analysis


sql
-- Understand data skew
SELECT 
    column_name,
    COUNT(*) as frequency,
    COUNT(*) * 100.0 / (SELECT COUNT(*) FROM your_table) as percentage
FROM your_table
GROUP BY column_name
ORDER BY frequency DESC;

Friday: Performance Documentation

Note which queries were slow
Document table sizes
Plan optimization strategies

📖 Reading:

"SQL Performance Explained" - Chapters 5-7

📅 Week 11-12: Master Detective

"Advanced Investigation Techniques"

Daily Sessions:

Monday: Business Rule Discovery


sql
-- Find business constraints in data
SELECT 
    CASE 
        WHEN rule_column > threshold THEN 'Violation'
        ELSE 'Normal'
    END as rule_status,
    COUNT(*)
FROM your_table
GROUP BY rule_status;

Tuesday: Correlation Hunting


sql
-- Find relationships between columns
SELECT 
    column_a,
    column_b,
    COUNT(*) as occurrence_count
FROM your_table
GROUP BY column_a, column_b
ORDER BY occurrence_count DESC;

Wednesday: Data Evolution Analysis


sql
-- How has data changed over time?
SELECT 
    DATE_TRUNC('month', date_column) as month,
    AVG(numeric_column) as monthly_average,
    COUNT(*) as monthly_count
FROM your_table
GROUP BY DATE_TRUNC('month', date_column)
ORDER BY month;

Thursday: Advanced Pattern Matching


sql
-- Find complex patterns
WITH pattern_analysis AS (
    SELECT 
        *,
        LAG(status_column) OVER (ORDER BY date_column) as previous_status
    FROM your_table
)
SELECT 
    previous_status,
    status_column as current_status,
    COUNT(*) as transition_count
FROM pattern_analysis
GROUP BY previous_status, status_column
ORDER BY transition_count DESC;

Friday: Capstone Investigation

Pick the most mysterious aspect of your database
Design a complete investigation
Document findings and conclusions

📖 Reading:

"Database Internals" - Chapters 1-2

🎯 Daily 20-Minute Structure:

Minutes 1-2: Review yesterday's notes Minutes 3-15: Execute daily SQL practice Minutes 16-18: Document findings Minutes 19-20: Read assigned chapter

📊 Weekly Milestones:

Week 2: Can profile any table in 5 minutes
Week 4: Identify temporal patterns automatically
Week 6: Map database relationships confidently
Week 8: Spot data quality issues instantly
Week 10: Read execution plans effectively
Week 12: Conduct complete data investigations

🏆 Success Metrics:

By week 12, you should be able to:

✅ Take any unknown database and understand it in 30 minutes
✅ Spot performance problems before they become critical
✅ Ask intelligent questions about data architecture decisions
✅ Design investigations that actually solve business problems
✅ Communicate findings clearly to non-technical stakeholders

💡 Pro Tips for Success:

Use YOUR database - practice on real call center data
Document everything - build your knowledge base
Question assumptions - like you did with the queue theory!
Focus on understanding WHY - not just WHAT
Skip days if needed - consistency beats perfection

Remember: You already demonstrated detective thinking with the DeviceId/ExtNo investigation. This roadmap just builds systematic skills around that natural curiosity!

Monday, April 8, 2024

SQL PROMPT

🕵️‍♂️ SQL Detective Work - Mastering Data Investigation

📚 Essential Books (In Learning Order)

Level 1: SQL Investigation Fundamentals

Level 2: Data Analysis & Detective Skills

Level 3: System Analysis & Architecture

🔧 Core Detective Techniques

1. The "Data Fingerprinting" Method

2. The "Relationship Hunter" Pattern

3. The "Time Pattern Detective"

4. The "Outlier Spotter"

🎯 Mental Framework: "The 5 Whys of Data"

🔍 Your Detective Skillset Development Plan

Week 1-2: Pattern Recognition

Week 3-4: Temporal Analysis

Week 5-6: Data Quality Investigation

Week 7-8: Performance Detective Work

🛠️ Essential SQL Tools for Detectives

Window Functions (Your Swiss Army Knife)

CTEs for Complex Investigation

CASE Statements for Categorization

🎓 Practice Exercises

Exercise 1: Mystery Database

Exercise 2: Performance Detective

Exercise 3: Pattern Detective

🚀 Advanced Skills to Develop

1. Business Domain Knowledge

2. Statistics Fundamentals

3. System Architecture Understanding

💡 The Secret Sauce

🎯 Next Steps for You

📚 More Honest Book Recommendations:

For Actual SQL Detective Techniques:

For Data Analysis Thinking:

🕵️‍♂️ 20-Minute Daily SQL Detective Roadmap

📅 Week 1-2: Foundation Building

Daily 20-Minute Sessions:

📖 Reading (5 min/day):

📅 Week 3-4: Time Detective

Daily Sessions:

📖 Reading:

📅 Week 5-6: Advanced Relationships

Daily Sessions:

📖 Reading:

📅 Week 7-8: Outlier Detective

Daily Sessions:

📖 Reading:

📅 Week 9-10: Performance Detective

Daily Sessions:

📖 Reading:

📅 Week 11-12: Master Detective

Daily Sessions:

📖 Reading:

🎯 Daily 20-Minute Structure:

📊 Weekly Milestones:

🏆 Success Metrics:

💡 Pro Tips for Success: