Question

i have a mysql table category with a field events as varchar which its values is like this : 11,29,32.and this values referer to event table ID. ( so i can say : i have a several event ID from event table in category table)

So i want to select events from category like that :

 SELECT *
FROM                      
event e, category c                                                    
where e.event_id in (c.events)

But that not give the correct result instead when i put the values manually like :

   SELECT *
FROM                      
event e, category c                                                    
where e.event_id in (11,29,32)

I hope that’s clear,

Any help please

Answer 1

Part of your problem is the way that you have set up your tables. Typically you will have an events, category and then a join table between the two. You should not store data in a comma separated list to query against.

If you cannot alter your table structure, then you can use the MySQL function FIND_IN_SET():

SELECT *
FROM event e
INNER JOIN category c                                                    
  on find_in_set(e.event_id, c.events)

See SQL Fiddle with Demo

If you can alter your tables, then the structure should be:

create table events
(
  event_id int not null auto_increment primary key,
  event_name varchar(50) not null
);

create table category
(
  cat_id int not null auto_increment primary key,
  cat_name varchar(50) not null
);

create table events_category
(
   event_id int not null,
   category_id int not null,
   PRIMARY KEY(event_id, category_id),
   constraint fk_event 
    foreign key (event_id) references events (event_id),
   constraint fk_category 
    foreign key (category_id) references category (cat_id)
);

Then when you query the data you would use:

select *
from events e
left join events_category ec
  on e.event_id = ec.event_id
left join category c
  on ec.category_id = c.cat_id