How to Find Users with Multiple Payments on the Same Day Using SQL?

SQL Queries to Find Users with Multiple Payments on the Same Day

This article demonstrates how to identify users who made multiple payments on the same day using SQL, with an added refinement to consider only distinct ZIP codes. We'll use a PAYMENT table with columns for user_id, account_no, zip, and date.

Initial Query (Without Distinct ZIP Code):

The initial approach uses a GROUP BY and HAVING clause to count payments:

SELECT 
    user_id,
    COUNT(*) AS payment_count
FROM 
    PAYMENT
GROUP BY
    user_id,
    account_no,
    date
HAVING COUNT(*) > 1;

This query groups payments by user, account number, and date. The HAVING clause filters results to show only users with more than one payment on a given day using the same account.

Improved Query (With Distinct ZIP Code):

To ensure only distinct ZIP codes are considered, a subquery is introduced to select unique combinations of user, account, ZIP, and date before grouping and counting:

SELECT 
    user_id,
    account_no,
    date,
    COUNT(*) AS payment_count
FROM
    (SELECT DISTINCT
        user_id,
        account_no,
        zip,
        date
     FROM
        PAYMENT
    ) AS distinct_payments
GROUP BY
    user_id,
    account_no,
    date
HAVING COUNT(*) > 1;

This refined query first creates a distinct set of payment records using the subquery (distinct_payments). Then, it groups these distinct records and applies the HAVING clause to identify users with multiple payments on the same day, considering only distinct ZIP codes for each payment. This ensures that a user with multiple payments to the same account on the same day, but with different ZIP codes, will not be included in the results.

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