mySQL 删除唯一键约束

Question

I am not sure how drop unique key constraint in mySql.

create table Lesson
(
  lessonId            int not null auto_increment,
  friendlyId          varchar(255) not null,
  primary key (lessonId),
  unique key friendlyId (friendlyId)
);

I have tried this but its a syntax error for mySql:

alter table Lesson
drop constraint friendlyId;

Answer 1

Drop the index with the unique constraint and recreate the index without unique constraint.

ALTER TABLE table_name DROP INDEX index_name;
ALTER TABLE table_name ADD INDEX index_name (columns);

in your case:

ALTER TABLE Lesson DROP INDEX friendlyId;
ALTER TABLE Lesson ADD INDEX friendlyId (friendlyId);