Chapter 10: SQL in the Real World

SQL Is Everywhere

SQL is not just for database administrators. It’s a core skill across:

• Data science and machine learning: retrieving and cleaning training data
• Software and app development: powering backend systems
• Business analytics and BI: driving dashboards, reports, and KPIs
• Product management: investigating usage patterns and A/B test outcomes
• Marketing and growth: querying campaign effectiveness and user segments

Whether you work in tech, science, or business, SQL is a bridge between raw data and actionable insight.

Building a Portfolio with SQL

To prove your skills and gain confidence, start building a public or private SQL portfolio. Great starting points:

• Use public datasets (e.g. Kaggle, Google BigQuery public data)
• Analyze data relevant to your interests (sports, environment, education, health)
• Share your queries, dashboards, and visualizations on GitHub or a personal site

Example Projects:

• Analyzing air quality trends using EPA data
• Creating a dashboard on bike-share usage by city and time of day
• Simulating and querying a mock ecommerce or survey database

Knowing SQL Helps You Understand and Work With:

• Python (pandas/sqlalchemy): for data science workflows
• R (dbplyr, dplyr): for academic/statistical analysis
• dbt: for transformation in ELT pipelines
• BI tools like Tableau, Power BI, and Looker
• Cloud services like AWS RDS, BigQuery, Snowflake, and Azure SQL

SQL is the shared language between analysts, engineers, and decision-makers.

Common SQL Interview Tasks

Typical SQL interview questions test your ability to:

• Write joins, groupings, and subqueries
• Handle edge cases (e.g. NULL, duplicates)
• Calculate running totals, percentiles, or lag values
• Refactor complex queries with CTEs

Practice regularly on:

• LeetCode SQL section
• Mode Analytics SQL tutorials
• StrataScratch and DataLemur