Stage 2 · Lesson 2 of 6
SQL on someone else's data
Most customer problems live in their data, often in a warehouse such as Snowflake, BigQuery or Redshift. You need to explore an unfamiliar schema quickly: list the tables, count rows, find the keys, check date ranges and spot missing or odd values.
Then answer questions with joins, GROUP BY and window functions. Being able to test a claim like "most claims are late" with a query in five minutes changes a meeting. Profile data before you trust it, because column names lie: a status column can mean different things in two systems, and dates may be stored in different time zones.
Common trapbuilding on a sample that looks clean, then discovering the real table has duplicates, nulls and three spellings of the same country.
A question to check yourself, an AI practice session and 1 cheat sheet entry come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- CoursePaidGrokking Python Fundamentals
Design Gurus · Beginner · $50
A structured path to real Python fluency, the most common glue language in customer work
- CourseFreeCS50's Introduction to Programming with Python
Harvard University · Beginner
Free: Harvard's Python course, with file I/O, libraries and tests in the later weeks