Let's go to SQL. Suppose a table has duplicate rows. How would you remove the duplicates?

You can remove duplicates by keeping only one copy of each row. One way is to create a temporary table with DISTINCT rows:

CREATE TABLE temp AS

SELECT DISTINCT * FROM original_table;

Then drop the original and rename:

DROP TABLE original_table;

ALTER TABLE temp RENAME TO original_table;

Alternatively, if you need to delete in place and the table has a primary key or unique identifier, use a DELETE with a window function:

DELETE FROM original_table

WHERE id NOT IN (

SELECT MIN(id)

FROM original_table

GROUP BY col1, col2, col3 -- columns that define uniqueness

);

This keeps the row with the smallest id for each duplicate group. The first method is simpler but requires extra space; the second works directly on the table.