Do I need advanced SQL to attempt this?

This problem is labeled as Intermediate. You don’t need to be an expert, only comfortable with SQL and willing to experiment. If you get stuck, the hints and solution will help you along.

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Practice SQL Window Functions | Xorthax's Trading Post

Tables Used

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

orders

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

Expected Output

Column
customerid
transactiondate
amount
previouspayment

60. Payment Patterns Revealed

Track each customer's past and present payments using lag().

Xorthax is curious about payment patterns among his customers. For each payment made, show the current amount and the amount of the previous payment by the same customer.

Write Your Query

This problem is labeled as Intermediate. You don’t need to be an expert—just comfortable with SQL and willing to experiment. If you get stuck, the hints and solution will guide you step by step.

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.

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