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You have written SELECT in a lab and it felt easy. Then an interview asked for a window function and it really was not. 48 days closes that gap, with nothing to install.
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AcademyLevich Academy · Course 01
A real Postgres runs right here in your browser. You write the queries, we check them, and you always know exactly where you stand. One yearly subscription, and you can start in about a minute.
48 days · 241 problems · ₹5,999 ₹699 a year
For every customer, show their most recent order and how many days passed since the one before it.
SELECT customer_id, placed_at,
placed_at - lag(placed_at) OVER (
PARTITION BY customer_id ORDER BY placed_at
) AS since_previous
FROM orders;Most courses let you nod along and move on. Here the query actually runs. Write it your way, name the columns what you like, and it still passes.Get it wrong and you will know.
You have written SELECT in a lab and it felt easy. Then an interview asked for a window function and it really was not. 48 days closes that gap, with nothing to install.
Your SQL works and you quietly hope nobody asks why. You have meant to fix that for ages. Two hours a day, in order, and you stop guessing, including the bits interviews love.
Open today. You never have to plan anything. 48 days in order, each one building on the last.
Read it, then try it. Every lesson explains why it works, not just what to type. Then you write real queries against real data.
Find out straight away. Your query runs and we compare the result. If it is off, we tell you how it differs and let you fix it yourself.
What a database actually is · Data types and creating tables · Changing data: INSERT, UPDATE, DELETE · …
Getting rows out: SELECT, WHERE, ORDER BY · NULL: the thing that silently breaks queries · Aggregation: GROUP BY and HAVING · …
ANY, ALL, EXISTS and NOT EXISTS · Window functions: the idea · Ranking: ROW_NUMBER, RANK, DENSE_RANK · …
How a query actually runs, and reading EXPLAIN · Indexes: what they are and when they are ignored · Sargability, why your index is being ignored · …
The project: a parcel logistics report · Interview problems: warm-up · Interview problems: medium, part one · …
About a minute to start. Nothing to install.
SQL from zero to interview-ready
Every day has a goal, the concepts explained with worked examples, the mistakes to expect, and problems to solve against your own database. You never have to decide what to study.