Find Duplicate/Repeated Rows in a Table

Problem: Write a SQL query to find repeated (duplicate) rows in a table. Approach: Group by the column(s) that define a "duplicate" and use HAVING COUNT() > 1 to surface groups appearing more than once, e.g. SELECT col1, col2, COUNT() FROM table GROUP BY col1, col2 HAVING COUNT() > 1. To return the actual duplicate rows (not just the grouping key), join back to the original table on the grouping key, or use a window function like COUNT() OVER (PARTITION BY col1, col2) and filter where the count exceeds 1.