在mysql列中存储列表

Question

Each row on my mysql table represents a different item. Each item has a attribute used_by_classes which can be a list with more than one element and up to 9, such as "Scout,Spy,Pyro"

I wonder what is the overall best way to store that information.

I was storing it as a list like above on a table used_by_classes and exploding it with php.

$classes= explode(",", $used_by_classes);

But thats just unreliable and probably silly. Creating 9 separate columns is another alternative but complicates things further on. How would you deal with this ?

Answer 1

For multi-valued attributes, the normative pattern is to create a second table. Each row in the new table will store one value of the attribute.

If the first table is

item (id int unsigned primary key, ...)

The second table would be something like:

item_class
( id            INT UNSIGNED PRIMARY KEY
, item_id       INT UNSIGNED NOT NULL COMMENT 'FK ref item.id'
, used_by_class VARCHAR(20)  NOT NULL

We'd likely add a unique constraint on the (item_id, used_by_class) tuple. With InnoDB, we'd create a FOREIGN KEY constraint referencing the item table.

item
 id name 
--- -----
 11 Cake

item_class
 id item_id used_by_class
--- ------- ------------- 
412      11 Scout
413      11 Spy
414      11 Pyro
415      11 Demoman

Answer 2

I think you can also serialize that data at store them. and when when you fetch the record you can un-serialize them all.

item
id  name   used_by_class
--- ----- ---------------
11  Cake   {scout:Spy:pyro}

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