How to Find Duplicate Account Payments in SQL with and without ZIP Code Filtering?

Detecting Duplicate Account Payments in SQL Databases

This guide demonstrates how to use SQL to pinpoint duplicate payment records for a single user, both with and without ZIP code consideration.

Identifying Duplicate Payments (Without ZIP Code)

The following SQL query efficiently identifies instances where a user has multiple payments associated with the same account number:

<code class="language-sql">SELECT
  user_id,
  COUNT(*) AS payment_count
FROM
  PAYMENT
GROUP BY
  account_no,
  user_id,
  payment_date
HAVING
  payment_count > 1;</code>

This query groups payment records by account_no, user_id, and payment_date. The COUNT(*) function tallies payments for each group, and the HAVING clause filters results, showing only groups with more than one payment (duplicates).

Adding ZIP Code Filtering for Enhanced Accuracy

To ensure that only payments with distinct ZIP codes are considered as duplicates, we modify the query:

<code class="language-sql">SELECT
  user_id,
  account_no,
  payment_date,
  COUNT(*) AS payment_count
FROM
  (
    SELECT DISTINCT
      user_id,
      account_no,
      zip,
      payment_date
    FROM
      payment
  ) AS distinct_payments
GROUP BY
  user_id,
  account_no,
  payment_date
HAVING
  payment_count > 1;</code>

This improved query utilizes a subquery (distinct_payments) to select unique combinations of user_id, account_no, zip, and payment_date. The main query then groups and counts these distinct records, identifying duplicate payments only when they involve different ZIP codes. This approach provides a more precise analysis of duplicate payments.

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