Connecting 3 MySQL tables, what am I doing wrong

Question

I have a 3 tables with the following data in MySQL

table 表

id  |   groupId  |   name   |
-----------------------------
1   |      1     |   tag1   |
2   |      1     |   tag2   |
3   |      1     |   tag3   |
4   |      1     |   tag4   |

groupId column here is unimportant right now.

table 表

id  |      name      |
----------------------
1   |   practice 1   |
2   |   practice 2   |
3   |   practice 3   |
4   |   practice 4   |

and a bridge between the two ( table) 表）

id  |   practiceId   |   tagId    |
-----------------------------------
1   |       1        |      1     |
2   |       1        |      2     |
3   |       1        |      3     |
4   |       2        |      1     |

But when I try to use the query:

SELECT practice.name
FROM practice
INNER JOIN practiceTag ON practiceTag.practiceId = practice.id
INNER JOIN tags        ON practiceTag.tagId = tags.id
WHERE (tags.id =  "1"
AND tags.id =  "2"
AND tags.id =  "3")

it doesn't return anything. And thats ok, since I know my query is kinda messed up. But thats as closest as I can get to show you, what I would like my query to do.

I've searched the forums and find out that I can use a group_concat. But I just can't get it to work.

Any help would be appreciated.

Thanks, Sebastian

Answer 1

You in clause not and

SELECT practice.name
FROM practice
INNER JOIN practiceTag ON practiceTag.practiceId = practice.id
INNER JOIN tags        ON practiceTag.tagId = tags.id
WHERE  tags.id  in ( '1', '2', '3') ;

if the id is numeric

SELECT practice.name
FROM practice
INNER JOIN practiceTag ON practiceTag.practiceId = practice.id
INNER JOIN tags        ON practiceTag.tagId = tags.id
WHERE  tags.id  in ( 1, 2, 3) ;

the query is equivalent

SELECT distinct practice.name
FROM practice
INNER JOIN practiceTag ON practiceTag.practiceId = practice.id
INNER JOIN tags        ON practiceTag.tagId in (1,2,3)

And if you want only the practice.name when all the 3 tagsId match the you should use temp table for getting the join table

    SELECT distinct practice.name
    FROM practice
    inner join (
        select practiceId from
        ( select distinct  practiceTag.practiceId as praticeId, practiceTag.tagId as tagId
         from tags  ) as t1
        where  tagId in (1,2,3)
        having count(*) > 2
        group by praticeId ) as t2;

Answer 2

I think your tags.id column is integer not string, so your sql query would be like this:

SELECT practice.name
FROM practice
INNER JOIN practiceTag ON practiceTag.practiceId = practice.id
INNER JOIN tags        ON practiceTag.tagId = tags.id
WHERE tags.id in (1,2,3);

Answer 3

In your WHERE part you ask for results that have id 1, 2 and 3 at the same time.

Replace the AND in your WHERE with OR