Tables Used

customers

Column	Type
customerid	bigint
name	text
species	text
contactinfo	text
loyaltystatus	text
joindate	text

orders

Column	Type
orderid	bigint
customerid	bigint
orderdate	timestamp without time zone
totalamount	double precision
status	text

transaction

Column	Type
transactionid	bigint
orderid	bigint
customerid	bigint
supplierid	bigint
transactiontype	text
amount	double precision
currencyid	bigint
transactiondate	text
paymentmethod	text
description	text
status	text
createdat	text
updatedat	text

Expected Output

Column
species
firsttransactiondate

Species Transaction Origins :Find the Earliest Recorded Transaction Date for Each Customer Species Intermediate

Q: Do I need advanced SQL to attempt this?

This problem is labeled as Intermediate. It assumes you’ve written a few window function queries before, but you don’t need to be an expert. Use the hints and explanations if you get stuck — they’re there to help you think through the logic.

Identify the first transaction date for customers of each species.

Xorthax is curious about the first transaction date for customers of each species. Write a query to display the first transaction date for each species.

Write Your Query

Answer:

          with species_transactions as
  (select c.species,
          t.transactiondate
   from orders o
   join transaction t on o.orderid = t.orderid
   join customers c on o.customerid = c.customerid)
select distinct species,
                first_value(transactiondate) over (partition by species
                                                   order by transactiondate asc) as firsttransactiondate
from species_transactions;

This represents analyzing customer transaction data to determine the first recorded activity by group or demographic segment.

You’ll practice grouping data logically, ordering results, and isolating the earliest event within each category.

This problem is labeled as Intermediate. It assumes you’ve written a few window function queries before, but you don’t need to be an expert. Use the hints and explanations if you get stuck — they’re there to help you think through the logic.

Yes. Every problem comes with optional hints you can reveal one at a time, plus a fully worked step-by-step solution. You decide how much help you want while practicing.

All problems on PracticeWindowFunctions.com are completely free and can be solved without creating an account. Right now there are over 80 practice problems, with new ones added regularly.

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Tables Used

Expected Output

Species Transaction Origins :Find the Earliest Recorded Transaction Date for Each Customer Species Intermediate

Identify the first transaction date for customers of each species.

What real-world scenario does this represent?

What SQL concepts will I practice here?

Do I need advanced SQL to attempt this?

Will I get hints and step-by-step explanations if I get stuck?

Are the problems free to access, and how many are available?

Ace the Data Science Interview