?? Ace Your Next Data Analysis Interview with SQL!

Question: "How can you identify duplicate records in a table, and how would you retrieve only those duplicates?"

Answer: To identify duplicate records, you can use the GROUP BY clause with an aggregate function like COUNT(). For example:

SELECT column_name, COUNT(*)

FROM table_name

GROUP BY column_name

HAVING COUNT(*) > 1;

?? This query groups the data by a specific column (or columns) and filters for records that appear more than once.

To retrieve the full details of the duplicate rows, you can use this query:

WITH CTE AS (

SELECT column_name, COUNT(*) AS cnt

FROM table_name

GROUP BY column_name

HAVING COUNT(*) > 1

)

SELECT t.*

FROM table_name t

JOIN CTE c

ON t.column_name = c.column_name;

Have you come across this question before? How did you tackle it? Let’s discuss in the comments!

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