CODEWITHSUNDEEP
mysql
swissdude
swissdude

Reputation:

Select from table depending on entries in other table

This is the setup:

Table A has a connection to table B. There are multiple entries (0 to n) in table B that can have a matching record in table A.

How do I form a query that gives me a record from table A only if a certain amount of matching records exist in table B?

Example:

Table A has clothing in it. Table B has attributes for clothing.

Table B has a foreign key to table A so it would look something like this:

id  fid_clothing1  attributeA
id  fid_clothing1  attributeB
id  fid_clothing1  attributeC
id  fid_clothing2  attributeA
id  fid_clothing2  attributeB

Now, I want only the clothes which have attribute attributeA AND attributeB AND attributeC. This is not a problem if I do a OR-query but I can't just do something like:

SELECT * from tableA
LEFT JOIN tableB on tableB.fid_cloting = tableA.id
WHERE attribute='A' AND attribute='B' AND attribute='C'

This condition will never evaluate to true. How do I do that?

Upvotes: 5

Views: 5209

Answers (4)

pjp
pjp

Reputation: 17629

You could do it with 3 inner joins... i.e. give me table A rows that have the attributes I want

SELECT A.id FROM tableA A
INNER JOIN tableB BA ON A.id = BA.fid_clothing AND BA.Attribute='A'
INNER JOIN tableB BB ON A.id = BB.fid_clothing AND BB.Attribute='B'
INNER JOIN tableB BC ON A.id = BC.fid_clothing AND BC.Attribute='C'
GROUP BY A.id

Upvotes: 2

butterchicken
butterchicken

Reputation: 13883

I would use GROUP_CONCAT to fetch a single row of all attributes for a given piece of clothing:

SELECT id,GROUP_CONCAT(attribute order by attribute) as Attributes 
FROM tableB 
GROUP BY id;

Giving something like:

| id | Attributes |
|  1 | A,B,C      |

From this resultset, you could select those ids for which the concatenated attribute matched the set of attributes you were looking for.

select id from MyConcatenatedResults where Attributes = 'A,B,C'

Upvotes: 1

Dave Rix
Dave Rix

Reputation: 1679

Another way to do this is as follows, which requires zero joins, but a nested sub-query... have tries this on a dummy database, and it seems to do the job. Hope it helps.

SELECT * 
FROM tableA A 
WHERE id IN ( 
              SELECT clothing_id
              FROM tableB B
              WHERE
                attribute =  "A"
                OR attribute =  "B"
                OR attribute =  "C"
              GROUP BY clothing_id
              HAVING count(*) = 3
            )

Upvotes: 0

Puran
Puran

Reputation: 994

May be this one.. have to try it 

SELECT * FROM TABLEA a, TABLE b 
WHERE a.id = b.clothing_id 
AND a.id in (SELECT clothing_id from TABLEB where attribute = 'A' AND clothing_id = a.id
UNION select clothing_id from TABLEB where attribute = 'B' AND clothing_id = a.id
UNION select clothing_id from TABLEB where attribute = 'C' AND clothing_id = a.id)

Upvotes: 0

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