Mysql delete constraint -


i have table below structure :

    create table `lm_help` (  `id` int(10) not null auto_increment,  `section` int(10) not null,  `language` int(10) not null,  `title` varchar(255) not null,  `text` text not null,  `timestamp` timestamp not null default current_timestamp,  primary key (`id`),  unique key `unique_help` (`section`,`language`),  key `language_constraint` (`language`),  constraint `language_constraint` foreign key (`language`) references `lm_languages` (`id`),  constraint `section_constraint` foreign key (`section`) references `lm_help_sections` (`id`) ) engine=innodb auto_increment=4 default charset=latin1

i need remove "unique_help" key, getting foreign key constraint error.

due error not able remove among these, section_constraint, language_constraint, unique_help.

below other tables refer :

create table `lm_languages` (  `id` int(11) not null auto_increment,  `name` varchar(255) not null,  `code` varchar(255) not null,  `status` int(11) default null,  `created_at` datetime not null,  `updated_at` datetime not null,  primary key (`id`) ) engine=innodb auto_increment=6 default charset=latin1     create table `lm_help_sections` (  `id` int(11) not null auto_increment,  `name` varchar(255) not null,  primary key (`id`) ) engine=innodb auto_increment=2 default charset=latin1

the problem unique_help (section, language) index used section_constraint foreign key constraint. can't drop index without dropping constraint first.

one way solve this, drop foreign key constraint first, drop index.

then can add (simple) index on (section) , recreate foreign key.

all these can done in 1 statement:

alter table lm_help     drop foreign key section_constraint,   -- drop fk     drop index unique_help,                -- index can dropped                                            -- ,     add index section_ix (section),        -- add new index     add constraint section_fk              -- fk can recreated         foreign key (section)          references lm_help_sections (id)   ;

tested @ sql-fiddle

improvement

i wrong, no need drop , recreate constraint. index can dropped, long new index created:

alter table lm_help     drop index unique_help,     add index section_ix (section)    ;

tested @ sql-fiddle-2


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