Question 1

Do I need to finish LDS SQL 50 first?

Accepted Answer

**No, but it helps.**

LDS SQL 50 introduces every pattern at least once across its 50 problems; this deep dive then **drills exclusively on window functions** across 30 focused exercises.

*If you struggled with Stage 3 of SQL 50 (the windows stage), this collection is exactly the remediation.*

Question 2

Why does this collection not include DENSE_RANK?

Accepted Answer

**Honest answer:** our reference solution pool currently has *zero* DENSE_RANK examples.

Per our 100/100 quality bar, **we never claim a pattern we don't actually teach**.

The **RANK vs ROW_NUMBER** distinction (Stages 1 and 2) covers the tie-handling concept that DENSE_RANK varies — conceptually you'll know what DENSE_RANK does after this collection, even without a dedicated exercise.

Question 3

What about LEAD, PERCENT_RANK, CUME_DIST?

Accepted Answer

**LEAD is structurally identical to LAG** (different direction). Once you complete Stage 3, LEAD is trivial.

**PERCENT_RANK and CUME_DIST** are rarely asked in real interviews and aren't in our current solution pool.

*The window functions taught here cover 95%+ of real interview questions.*

Question 4

How is this different from LeetCode's SQL window questions?

Accepted Answer

**LeetCode's window function problems use toy 2-3 column tables.**

Our 30 problems run on **8-15 table production schemas** modeled after Uber, Stripe, Netflix, and Airbnb.

*You'll learn windows in the context of real multi-table queries, not in isolation.*

Question 5

How long does it take to complete?

Accepted Answer

**~12 hours of focused work.** Most users finish in 2 weeks at 2 problems per day.

**Stage 5 (Top-N per group) is the densest** — give yourself ~25 minutes per problem there.

Question 6

What SQL dialect is this?

Accepted Answer

**SQLite-compatible by default**, with **PostgreSQL mode** available.

All window function syntax shown works *identically on BigQuery, Snowflake, and Redshift.*

Question 7

How does this compare to DataLemur, StrataScratch, or LeetCode for window functions?

Accepted Answer

Window functions are taught everywhere — usually as isolated pattern drills.

**What LDS SQL Window Functions 30 gives you that they don't:**

- **A 6-stage curriculum** covering every window pattern that actually appears in interviews: `ROW_NUMBER`, `RANK`, `LAG`, running totals, moving averages, partitioned Top-N, and NTILE quartile bucketing
- **Multi-window composition per problem** — most problems compose 2–3 window functions in a single query, the realistic interview shape
- **Real time-series data** on industry schemas — payments, sessions, ad events, support tickets — not toy 10-row tables
- **Both SQLite and PostgreSQL** on every problem
- **Built-in SQL Visualizer** that walks through each window's frame visually

*Catalogs teach the syntax. This collection teaches the composition.*

LDS SQL Window Functions 30

About this collection

Your Learning Path

Why These 30?

Every Window Pattern, Composed

Multi-Window Composition Per Problem

Real Time-Series Data on Industry Schemas

Skill Coverage

FAQ

Ready to Master SQL?

LDS SQL Window Functions 30

About this collection

Your Learning Path