Table with multiple items in one field - mysql

Question

I'm pretty much a MySql newbie so sorry if this sounds daft or I ramble off topic.
I am building a table to list all the data about exhibitions. This comprises fields with data like venue, dates, times, etc and one field with a list of items exhibited. This field will have a delimited list of numbers. They will between 1 and 50 numbers in the range 1 to 999, currently the num_max is 170.
I realise that it would be better practice to hold this data in separate tables but that complicates the uploading process, would require a new table being created for each new exhibition and give rise to more opportunity for errors.
Assuming that this strategy is correct, my real problem is in processing the data.
How do I extract the list of numbers then use it to get an array of product numbers from the master product table?

Answer 1

You should only need one more table that holds items to be included in an exhibit. This table could have several rows for one exhibit, like so:
exhibit_id item_id description
______________________________________________
1 1 painting
1 2 statue
Then, all you would need to do is join the two tables together.
Otherwise, if you did not want to do this, use the php explode method to turn a delimited string into an array.
$data = mysql_query($query);
while ($row = mysql_fetch_assoc($result)) {
$items = $row['items'];
//the explode method in php allows you to turn a delimited string into an array.
$items_array = explode(',', $items);
//loop through each of the items in this exhibit
foreach($items_array as $current_item) {
//do something with $current_item
}
}

Answer 2

If you are going to hold a field that has data such as "2,45,67,126" then you're going to have to process that using the language in which you're extracting it, perhaps PHP.
The 'real' solution would be to have a unique identifier on the table holding the exhibitions and have a second table with the items. So for example, you'd have an id of '42' for the exhibition then a second table (called, perhaps 'items') holding:
id item
42 2
42 45
42 67
42 126
That shouldn't complicate your upload process too much and then you can easily return all the items in an exhibition using:
SELECT item FROM items WHERE id=$exhibition_id

Answer 3

Actually, it wouldn't require a new table for each exhibit, just adding rows to an existing table.
The rows in the child table would be "related" to the parent table by a foreign key.
For example
exhibit
( id int auto_increment primary key comment 'PK unique identifier for exhibit'
, exhibit_venue
, exhibit_date
et al.
)
exhibit_item
( exhibit_id int comment 'fk to exhibit.id'
, item_id int comment 'fk to item.id'
, primary_key (exhibit_id, item_id)
, foreign_key exhibit_items_fk1 (exhibit_id) references exhibit (id)
, foreign_key exhibit_items_fk2 (item_id) references item (id)
)
item
( id int auto_increment primary key comment 'PK unique identifier for item'
, name
, description
, size
, weight
et al.
)
exhibit
id venue date
---- ------- -----------
123 Fox 2014-02-24
124 Ice 2014-03-01
item
id name description
---- -------- -----------
41 madonna painting
42 david sculpture
43 mona lisa painting
exhibit_item
exhibit_id item_id
---------- -------
123 41
123 42
123 43
If you need to store a relative sequence or position (relative order) of the items within an exhibit, you can add another attribute to the exhibit_item table, to store an integer representing the position.
To get all items for one exhibit:
SELECT i.id
, i.name
, i.description
FROM exhibit_item s
JOIN item i
ON i.id = s.item_id
WHERE s.exhibit_id = 123
ORDER BY s.position
If it's handier for you to return a comma separated list of the item ids within an exhibit, as a single string...
SELECT GROUP_CONCAT(s.id ORDER BY s.position) AS item_list
FROM exhibit_item s
WHERE s.exhibit_id = 123