Check out example codes for "how to remove unique key constraint in mysql". It will help you in understanding the concepts better.

Code Example 1

ALTER TABLE tbl_name DROP INDEX index_name

Code Example 2

DROP INDEX index_name ON tbl_name

Code Example 3

ALTER TABLE mytable DROP INDEX key_Name;

Code Example 4

ALTER TABLE tbl_quiz_attempt_master
  DROP INDEX `PRIMARY`;

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