constraints - Mysql Create Index Set As No Duplicates -

i have table p_places has 2 columns both foriegn keys references parent tables:

mysql> create table p_places(     -> user_id int not null,     -> place_id int not null,     -> foreign key(user_id) references people(user_id) on delete cascade,     -> foreign key(place_id) references places(place_id) on delete cascade     -> )engine=innodb; 

i trying create index both of columns there can not duplicate rows(there can duplicate foriegn keys however...just not rows).

i tried:

alter table p_places add index(user_id+place_id no duplicate);  alter table p_places add unique index(user_id+place_id);  alter table p_places add unique index both_id(user_id+place_id); 

but had no success. try alter table command learning purposes rather creating table.

you close want.

alter table p_places add constraint tb_unique unique(user_id, place_id) 

• purpose of naming constraint