I’m working with a MySQL database that has a table containing a text column (varchar type). I need to write a SQL query that will help me locate all rows where the same value appears multiple times in this specific column.
For example, if I have names like ‘John’, ‘Mary’, ‘John’, ‘Bob’, ‘Mary’ in my column, I want to find which names are repeated and see all the records that contain those duplicate values.
What would be the most efficient SQL query approach to accomplish this task? I’m looking for a solution that shows me both the duplicate values and the actual records containing them.
Here’s a cleaner approach using ROW_NUMBER(): SELECT * FROM (SELECT *, ROW_NUMBER() OVER (PARTITION BY column_name ORDER BY id) as rn FROM your_table) t WHERE column_name IN (SELECT column_name FROM your_table GROUP BY column_name HAVING COUNT(*) > 1). You get way more control over ordering, especially when you need duplicates in a specific sequence. I used this with customer data where I had to keep duplicate entries in chronological order. Window functions don’t add much overhead compared to basic GROUP BY either.
Use a subquery to find duplicates first, then grab all matching records. Here’s the query: SELECT * FROM your_table WHERE column_name IN (SELECT column_name FROM your_table GROUP BY column_name HAVING COUNT(*) > 1). I’ve run this on large production datasets and it performs pretty well. The subquery finds values that appear more than once, then the outer query pulls everything that matches. Just make sure you’ve got an index on that column if you’re dealing with big tables.