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You can use the "DISTINCT" keyword in your SELECT statement to ensure that only unique rows for a particular value are returned. For example:

SELECT DISTINCT columnname FROM tablename;

This will return only unique values in the specified column. If you want to ensure that only unique rows for a combination of values are preserved, you can use the "GROUP BY" statement in conjunction with "DISTINCT". For example:

SELECT column1, column2 FROM tablename GROUP BY column1, column_2;

This will group the results by the combination of column 1 and column 2, and then return only the unique combinations.