SQL

Identifying Duplicate Records Using Window Functions

Detect duplicate entries within a dataset based on one or more columns using SQL window functions like ROW_NUMBER(), useful for data cleaning and integrity.

WITH RankedItems AS (
    SELECT
        id,
        email,
        username,
        ROW_NUMBER() OVER(PARTITION BY email ORDER BY created_at) as rn
    FROM
        users
)
SELECT
    id,
    email,
    username
FROM
    RankedItems
WHERE
    rn > 1;
How it works: This query identifies duplicate records in the `users` table based on the `email` column. The `ROW_NUMBER() OVER(PARTITION BY email ORDER BY created_at)` window function assigns a sequential number to each row within groups defined by the `email`. If `rn` is greater than 1, it indicates that the row is a duplicate within its `email` group, ordered by `created_at` to prioritize the original entry.

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