SQL Select only rows where multiple relationships exist

Question

Given a parent table 'parent'

╔═══════════╦══════════╗
║ PARENT_ID ║   NAME   ║
╠═══════════╬══════════╣
║         1 ║ bob      ║
║         2 ║ carol    ║
║         3 ║ stew     ║
╚═══════════╩══════════╝

and a many-many relationship table 'rel' between parent and a (here unspecified) property table

╔═══════════╦═══════════╗
║ PARENT_ID ║  PROP_ID  ║
╠═══════════╬═══════════╣
║         1 ║         5 ║
║         1 ║         1 ║
║         2 ║         5 ║
║         2 ║         4 ║
║         2 ║         1 ║
║         3 ║         1 ║
║         3 ║         3 ║
╚═══════════╩═══════════╝

How can I select all parents that have all of a specified set of relationships? E.g. with the sample data, how can I find all parents that have both property 5 and 1?

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edit: Same question but with requirement for an exact match: SQL Select only rows where exact multiple relationships exist

Answer 1

This is called Relational Division

SELECT  a.name
FROM    parent a
        INNER JOIN rel b
            ON a.parent_ID = b.parent_ID
WHERE   b.prop_id IN (1,5)
GROUP BY a.name
HAVING COUNT(*) = 2

• SQLFiddle Demo Link

UPDATE 1

if unique constraint was not enforce on prop_id for every parent_id, DISTINCT is needed on this case.

SELECT  a.name
FROM    parent a
        INNER JOIN rel b
            ON a.parent_ID = b.parent_ID
WHERE   b.prop_id IN (1,5)
GROUP BY a.name
HAVING COUNT(DISTINCT b.prop_id) = 2

Answer 2

I just saw this solution to a different question that seems to fit this case:

 SELECT distinct parent_id
 FROM rel as T1
 INNER JOIN rel as T2
 ON T1.parent_id = T2.parent_id
 WHERE T1.prop_id = '1' and T2.prop_id = '5'

Answer 3

I've written your table in to a CTE, let me know if you require assistance in adapting the code for your purposes.

;WITH MyTable AS
(
    SELECT   parent_id = 1
            ,prop_id = 5    UNION ALL
    SELECT 1,1              UNION ALL
    SELECT 2,5              UNION ALL
    SELECT 2,4              UNION ALL
    SELECT 2,1              UNION ALL
    SELECT 3,1              UNION ALL
    SELECT 3,3              
)
,Eval AS
(
    SELECT   parent_id
            ,PropEval   = SUM(CASE WHEN prop_id IN (1,5) THEN 1 ELSE 0 END)
    FROM MyTable
    GROUP BY parent_id
)
SELECT parent_id
FROM Eval
WHERE PropEval = 2