How do I delete duplicate rows and keep the first row?

Backup your data, then...

MySQL supports JOINs in DELETE statements. If you want to keep the first of the duplicates:

DELETE a  FROM MYVIEWS a  JOIN (SELECT MIN(t.a1) AS min_a1, t.k1, t.k2, t.k3          FROM MYVIEWS t      GROUP BY t.k1, t.k2, t.k3        HAVING COUNT(*) > 1) b ON b.k1 = a.k1                              AND b.k2 = a.k2                              AND b.k3 = a.k3                              AND b.min_a1 != a.a1

If you want to keep the last of the duplicates:

DELETE a  FROM MYVIEWS a  JOIN (SELECT MAX(t.a1) AS max_a1, t.k1, t.k2, t.k3          FROM MYVIEWS t      GROUP BY t.k1, t.k2, t.k3        HAVING COUNT(*) > 1) b ON b.k1 = a.k1                              AND b.k2 = a.k2                              AND b.k3 = a.k3                              AND b.max_a1 != a.a1

You can create a new table with the same structure but empty, then create the unique key on it, then do a INSERT IGNORE / SELECT * FROM the original table into the new table, then delete the original table.

INSERT IGNORE will automatically ignore any primary or unique key issues and just skip the duplicates.

Someting like this?

DELETE FROM myviews WHERE EXISTS(SELECT CONCAT(k1, k2, k) AS dup_valueFROM myviewsGROUP BY dup_valueHAVING (COUNT(dup_value) > 1));