Multiple records in a table matched with a column - sql

Question

The architecture of my DB involves records in a Tags table. Each record in the Tags table has a string which is a Name and a foreign kery to the PrimaryID's of records in another Worker table.
Records in the Worker table have tags. Every time we create a Tag for a worker, we add a new row in the Tags table with the inputted Name and foreign key to the worker's PrimaryID. Therefore, we can have multiple Tags with different names per same worker.
Worker Table
ID | Worker Name | Other Information
__________________________________________________________________
1 | Worker1 | ..........................
2 | Worker2 | ..........................
3 | Worker3 | ..........................
4 | Worker4 | ..........................
Tags Table
ID |Foreign Key(WorkerID) | Name
__________________________________________________________________
1 | 1 | foo
2 | 1 | bar
3 | 2 | foo
5 | 3 | foo
6 | 3 | bar
7 | 3 | baz
8 | 1 | qux
My goal is to filter WorkerID's based on an inputted table of strings. I want to get the set of WorkerID's that have the same tags as the inputted ones. For example, if the inputted strings are foo and bar, I would like to return WorkerID's 1 and 3. Any idea how to do this? I was thinking something to do with GROUP BY or JOINING tables. I am new to SQL and can't seem to figure it out.

Answer 1

This is a variant of relational division. Here's one attempt:
select workerid
from tags
where name in ('foo', 'bar')
group by workerid
having count(distinct name) = 2

Answer 2

You can use the following:
select WorkerID
from tags where name in ('foo', 'bar')
group by WorkerID
having count(*) = 2
and this will retrieve your desired result/
Regards.

Answer 3

This article is an excellent resource on the subject.
While the answer from #Lennart works fine in Query Analyzer, you're not going to be able to duplicate that in a stored procedure or from a consuming application without opening yourself up to SQL injection attacks. To extend the solution, you'll want to look into passing your list of tags as a table-valued parameter since SQL doesn't support arrays.
Essentially, you create a custom type in the database that mimics a table with only one column:
CREATE TYPE list_of_tags AS TABLE (t varchar(50) NOT NULL PRIMARY KEY)
Then you populate an instance of that type in memory:
DECLARE #mylist list_of_tags
INSERT #mylist (t) VALUES('foo'),('bar')
Then you can select against that as a join using the GROUP BY/HAVING described in the previous answers:
select workerid
from tags inner join #mylist on tag = t
group by workerid
having count(distinct name) = 2
*Note: I'm not at a computer where I can test the query. If someone sees a flaw in my query, please let me know and I'll happily correct it and thank them.