MySQL Duplicating Row Results in Table When Searching Across Multiple Tables - php

Question

I have three tables in a mySQL db one for users, one for colours and one for the linking of the users to the colours
Table 1 users
==============
ID | Name
--------------
1 | John
2 | Jayne
3 | Fred
Table 2 colours
==============
ID | Colour
--------------
1 | Blue
2 | Red
3 | Yellow
Table 3 link
==============
ID | Name | Colour
--------------
1 | 1 | 1
2 | 1 | 2
3 | 2 | 1
4 | 3 | 2
5 | 3 | 3
As you can see, some users have more than one favourite colour (yeah, i know, how annoying).
At the moment, I can show them in a table, with their favourite colour(s) in a column.
BUT, I want to be able to filter the table results by colour.
I can do it no problem with having a filter of just one colour, BUT the problem comes along with two colours.
If I want to see which user has selected for example Blue AND Red, I get a result of zero.
How can I get this result, without creating a search which results in each row being dedicated to a colour and then in turn showing the same user twice (one for red one for blue).
I hope this makes sense
THANKS IN ADVANCE
EDIT
An example query I have used is
SELECT * FROM users, colours, link WHERE users.id = link.name AND link.colour = colours.id
Alternatively to show for specific colour
SELECT * FROM users, colours, link WHERE users.id = link.name AND link.colour = colours.id AND link.colour = 1
But for double filter which shows duplicates
SELECT * FROM users, colours, link WHERE users.id = link.name AND link.colour = colours.id AND link.colour = 1 OR link.colour = 2

Answer 1

If that looks right here is the code:
SELECT Name FROM users
WHERE ID IN (SELECT DISTINCT(Name) AS Name
FROM link L
WHERE 2 IN (SELECT Colour FROM link L2 WHERE L.Name = L2.Name)
AND 1 IN (SELECT Colour FROM link L2 WHERE L.Name = L2.Name))
And now let me try to explain what L and L2 are... First sorry for my English I'll do my best to make a sense for you...
We make subquery on the same table here so we need to use alias for the table. Alias we use to give temporary name table or column which will be used only for that query.
Example for alias is when we select some column from table (Price and Quantity) and let's say we want to calculate Price * quantity and SELECT that column as total (total will be the name of that column in table which we return after we execute the query). Column name total well be give alias. we crate alias like:
SELECT Price, Quantity, (Price * Quantity) AS **total**
FROM t1...
That will return table with three column Price, Quantity, Total... if we don't use this AS total the name of that column will be Price * Quantity...
So here we use L and L2 just to know which column Name is from which part of SELECT query. If we wouldn't use alias in subquery
SELECT Colour FROM link L2 WHERE L.Name = L2.Name
we would have problem because subquery which locks like this:
SELECT Colour FROM link WHERE Name = Name
Doesn't make a a lot of sense, isn't it?
So basically we temporary rename table in this query because we need to know which column from which table we compere whit other one, in other way database will have a problem what to select...
I hope this make a sense for you. If you have any further question fill free to ask I will do my best to try to explain it to you.
I hope i didn't make it more complicated than it is...
GL!
EDIT
Hi there again, i worked something and and i figured out that your question probably have better answer than the first i give you... Hope it's not too late!
SELECT u.Name
FROM users u
INNER JOIN link L
ON u.ID = L.Name
INNER JOIN link l2
ON L.Name = L2.Name
WHERE L.Colour = 2 AND L2.Colour = 1
Look SQL Fiddle for that...