What database structure should be used to include table rows in multiple categories?

Question

I have a table within a MySQL database with various data in it (for the sake of example, let's give it the following:

ID   |   Place   |   Phone   |   Email   |   Category 

Now, I want to redesign the "Category" section to be able to include any given row in multiple (searchable) categories.

For example, let's say that there is a place called 'Lakeside Picnic Area.' Currently it is classified as 'Nature Reserve'. So, when people are searching for a nature reserve, it shows in their search results. However, I also want it to show up in "Food Area", "Wildlife", and "Viewing Point".

My question is this: How do I design my table/database structure to allow all of the data entries/rows to be searchable by multiple categories?

CONTINUATION: I don't suppose that anyone could help me to formulate the "Insert" command for my PHP could they?

Answer 1

You need a design like this:

Table: Places                                    Indexes:
+----+-----------+-------+------------------+    ID: Primary Key; Auto-Increment
| ID | Place     | Phone | Email            |    
+----+-----------+-------+------------------+
| 1  | Somewhere | 12345 | test@test.com    |
| 2  | SomePlace | 54321 | testing@test.com |
+----+-----------+-------+------------------+

Table: Categories                                 Indexes:
+-------------+-----------------+                 Category_id: Primary Key; Auto-Increment
| Category_id | Category_name   |
+-------------+-----------------+
| 1           | Test Category 1 |
+-------------+-----------------+


Table: Category_relationships                     Indexes:
+-------------+----------+-------------+          record_id: Primary Key; Auto-increment
| record_id   | place_id | category_id |          place_id: Foreign Key
+-------------+----------+-------------+          category_id: Foreign Key
| 1           | 1        | 1           |          place_id AND category_id: Unique
+-------------+------------------------+
| 1           | 2        | 1           |
+-------------+------------------------+

Then if you wanted to retrieve all the categories for place ID 1:

SELECT c.category_name 
FROM categories c 
INNER JOIN category_relationships cr 
    ON c.category_id = cr.category_id 
INNER JOIN places p
    ON cr.place_id = p.ID
WHERE p.ID = 1

Answer 2

This is called an n m relationship.

In other words, a place can have more than one category, and a category has more than one place.

Here's how you would model it.

Place
-----
Place ID
Place Name
Place Phone
Place Email

Category
--------
Category ID
Category Name

CategoryPlace
-------------
CategoryPlace ID
Category ID
Place ID

All three tables have an auto-incrementing int or long primary key.

The CategoryPlace table would have a unique index on (Category ID, Place ID). This allows you to find all of the places for a given category.

You can also have a unique index on (Place ID, Category ID). This allows you to find all the categories for a given place.

Answer 3

You need a Catagories table and a Place_category table.

The Catagories table will be something like:

Category_ID int,
Category_Name varchar

The Place_category table should be like:

Category_ID int
Places_ID int

Then you would enter one entry in the Place_category table for each category you want to assign to each place.

Answer 4

Simply use a new table with 2 columns :

1 column for the id of your item "Lakeside Picnic area" 1 column for a category id

Multiple category would the result in multiple lines in that table, with the same item id but with a different category id.

That way you can easily retrieve all the items for a given category, and all the categories for a given item. What you're trying to represent is called a many-to-many relationship, cause each category can have many items, and each item can have many categories.