再次记录一下：

DROP PROCEDURE IF EXISTS del_idx;

DELIMITER $

CREATE PROCEDURE del_idx(IN p_tablename VARCHAR(200), IN p_idxname VARCHAR(200))  

BEGIN  

DECLARE str VARCHAR(250);  

  SET @str=CONCAT(' drop index ',p_idxname,' on ',p_tablename);   

    

  SELECT COUNT(*) INTO @cnt FROM information_schema.statistics WHERE table_name=p_tablename AND index_name=p_idxname ;  

  IF @cnt >0 THEN   

    PREPARE stmt FROM @str;  

    EXECUTE stmt ;  

  END IF;  

  

END 

$

DELIMITER ;

CALL del_idx('table_name','idx_unique');  

ALTER TABLE table_name ADD UNIQUE idx_unique(column1,column2);