Mysql - select ids that match all tags

Question

I have a cross-reference table:

ID | tag
1  | 4
1  | 5
1  | 6
2  | 4
2  | 5
2  | 8
3  | 2

I need to select the IDs that match all of a

Answer 1

The idea of the query is that you need to match the number of records to the number of values you have provided in the WHERE clause.

SELECT ID
FROM tableName
WHERE tag IN (4, 8)
GROUP BY ID
HAVING COUNT(*) = 2

• SQLFiddle Demo

if unique constraint was not specified on tag for every ID, then DISTINCT is needed

SELECT ID
FROM tableName
WHERE tag IN (4, 8)
GROUP BY ID
HAVING COUNT(DISTINCT tag) = 2