SELECT
	a.*
FROM
	MessagesTable a
	INNER JOIN
	(
		SELECT Message_id FROM UsersTable WHERE user_name = 'user1'
		UNION 
		SELECT Message_id FROM GroupsTable WHERE group_name = 'group2'
	)b ON a.Message_id = b.Message_id

CREATE TABLE #MessagesTable(Message_id INT, Message_name VARCHAR(32));
CREATE TABLE #UsersTable (Message_id INT, [User_name] VARCHAR(32));
CREATE TABLE #MembershipTable (Message_id INT, Group_name VARCHAR(32));

INSERT INTO #MessagesTable VALUES (1,'One'),(2,'Two'),(3,'Three'),(4,'Four');
INSERT INTO #UsersTable VALUES(1,'User1'),(2,'User2');
INSERT INTO #MembershipTable VALUES (3,'Group1'),(4,'Group2');


SELECT
	a.*
FROM
	#MessagesTable a
	INNER JOIN
	(
		SELECT Message_id FROM #UsersTable WHERE user_name = 'user1'
		UNION 
		SELECT Message_id FROM #MembershipTable WHERE group_name = 'group2'
	)b ON a.Message_id = b.Message_id

DROP TABLE #MessagesTable;
DROP TABLE #UsersTable;
DROP TABLE #MembershipTable

quote:

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Originally posted by sunitabeck

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