Identifying and Deleting Duplicate Records While Retaining One

DELETE t1 FROM your_table t1
INNER JOIN your_table t2
WHERE t1.id < t2.id AND t1.column1 = t2.column1 AND t1.column2 = t2.column2;

How it works: This SQL snippet efficiently deletes duplicate records from 'your_table' while preserving one unique instance. It works by joining the table with itself ('t1' and 't2'). It identifies duplicates where 'column1' and 'column2' are identical, but 't1.id' is less than 't2.id'. This condition ensures that for every pair of duplicates, the row with the smaller 'id' (often signifying an older record) is targeted for deletion, thus keeping the newer (or higher 'id') duplicate.