How to select all relations that current user is involved in ? ASP.NET SQL Server - sql

Question

I have this database with users and relations. I simply want to show username, firstName and lastName of all the relations that some specific (current logged in user) userID is present in. How do I do this?
This is my best try.
SELECT
UserRelationship.relationshipType,
UserRelationship.userFirstID, UserRelationship.userSecondID,
[User].username, [User].firstName, [User].lastName
FROM
[User]
INNER JOIN
UserRelationship ON [User].userID = UserRelationship.userFirstID
AND UserRelationship.relationshipType = 'friends'
OR [User].userID = UserRelationship.userSecondID
AND UserRelationship.relationshipType = 'friends'
WHERE
([User].userID = #userID)
This returns all relations, but the username, firstname and lastname of current user.
These are my tables:
CREATE TABLE [dbo].[UserRelationship]
(
[userFirstID] INT NOT NULL,
[userSecondID] INT NOT NULL,
[initiatedBy] NVARCHAR (50) NOT NULL,
[relationshipType] NVARCHAR (50) NOT NULL,
CONSTRAINT [PK_UserRelationship]
PRIMARY KEY CLUSTERED ([userFirstID] ASC, [userSecondID] ASC),
CONSTRAINT [FK_UserRelationship_userFirstID]
FOREIGN KEY ([userFirstID]) REFERENCES [dbo].[User] ([userID]),
CONSTRAINT [FK_UserRelationship_initiatedBy]
FOREIGN KEY ([initiatedBy]) REFERENCES [dbo].[User] ([username]),
CONSTRAINT [CK_UserRelationship_relationshipType]
CHECK ([relationshipType]='pending' OR [relationshipType]='friends')
);
and
CREATE TABLE [dbo].[User]
(
[userID] INT IDENTITY (1, 1) NOT NULL,
[username] NVARCHAR (50) NOT NULL,
[firstName] NVARCHAR (50) NULL,
[lastName] NVARCHAR (50) NULL,
[dateOfBirth] DATE NULL,
[city] NVARCHAR (50) NULL,
[address] NVARCHAR (50) NULL,
[phoneNumber] INT NULL,
[email] NVARCHAR (50) NULL,
[rank] NVARCHAR (50) NULL,
[profilImage] NVARCHAR (255) NULL,
PRIMARY KEY CLUSTERED ([userID] ASC),
CONSTRAINT [AK_User_username]
UNIQUE NONCLUSTERED ([username] ASC)
);
In my UserRelationship table, I store all relations by always making sure userFirstID is lower than userSecondID. So I only have 1 record per relation.

Answer 1

Do you want to get the names of the users the current user has a friendship with? Then one possibility is to join the user's table again twice for each the first and the second id in the relationship's table and check in a CASE ... END which one is the other user and return their name.
SELECT UserRelationship.relationshipType,
UserRelationship.userFirstID,
UserRelationship.userSecondID,
[User].username,
[User].firstName,
[User].lastName,
CASE [User].[UserID]
WHEN OtherUser1.userId
THEN OtherUser2.userName
WHEN OtherUser2.userId
THEN OtherUser1.userName
END OtherUserUserName,
CASE [User].[UserID]
WHEN OtherUser1.userId
THEN OtherUser2.firstName
WHEN OtherUser2.userId
THEN OtherUser1.firstName
END OtherUserFirstName,
CASE [User].[UserID]
WHEN OtherUser1.userId
THEN OtherUser2.lastName
WHEN OtherUser2.userId
THEN OtherUser1.lastName
END OtherUserLastName
FROM [User]
INNER JOIN UserRelationship
ON [User].userID IN (UserRelationship.userFirstID,
UserRelationship.userSecondID)
AND UserRelationship.relationshipType = 'friends'
INNER JOIN [User] OtherUser1
ON OtherUser1.userID = UserRelationship.userFirstID
INNER JOIN [User] OtherUser2
ON OtherUser2.userID = UserRelationship.userSecondID
WHERE ([User].userID = #userID);
(Assuming a user cannot be a friend of themselves. That would require an extension of the CASE .... ENDs for the case of all three ids being equal.)