SQL Server 2022

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CREATE TABLE Reports (
    reportId INT,
    OrganizationID INT
);

CREATE TABLE Users (
    User_ CHAR(1),
    OrganizationId INT
);

INSERT INTO Reports (reportId, OrganizationID) VALUES
(1, 1), --ac
(1, 2), --ac
(2, 1), --ac
(3, 1), -- none
(3, 2), -- none
(3, 3); -- none

INSERT INTO Users (User_, OrganizationId) VALUES
('a', 1), -- 1,2
('a', 2), -- 1,2
('b', 2), -- none
('c', 1), -- 1,2
('c', 2), -- 1,2
('c', 4);
12 rows affected

SELECT
      r.reportId
    , u.User_
FROM Reports r
JOIN Users u ON r.OrganizationID = u.OrganizationId
GROUP BY
      r.reportId
    , u.User_
HAVING COUNT(DISTINCT r.OrganizationID) = (
        SELECT COUNT(DISTINCT OrganizationID)
        FROM Reports r2
        WHERE r2.reportId = r.reportId
        )


reportId
User_


1
a

1
c

2
a

2
c


    SELECT
          r.reportId
        , u.User_
    FROM reports r
    LEFT JOIN users u ON r.OrganizationID = u.OrganizationID
    -- where r.reportId = 1 -- optional where clause
    GROUP BY
          r.reportId
        , u.User_
    HAVING count(distinct u.OrganizationID) = count(distinct  r.OrganizationID)
    ORDER BY
          r.reportId
        , u.User_


reportId
User_


1
a

1
b

1
c

2
a

2
c

3
a

3
b

3
c


Warning: Null value is eliminated by an aggregate or other SET operation.