Conditionally drop a primary key from a table in MySQL (v. 5.6)

conditional_drop_pk.sql

-- Temporarily change delimiter to $$
DELIMITER $$
-- Drop procedure if it exists
DROP PROCEDURE IF EXISTS drop_pk_if_exists $$
-- Begin create procedure
CREATE PROCEDURE drop_pk_if_exists () BEGIN
  -- If my_table has a primary key
  IF EXISTS(select * from `information_schema`.`table_constraints`
              where `constraint_schema` = database()
              and `constraint_type` = "PRIMARY KEY"
              and `table_name` = "my_table") THEN
    BEGIN
      -- Drop the primary key
      ALTER TABLE `my_table` DROP PRIMARY KEY;
    END;
  END IF;
END $$
-- Reset delimiter back to ';'
DELIMITER ;
-- Call procedure
CALL drop_pk_if_exists();
-- Drop procedure
DROP PROCEDURE drop_pk_if_exists;