How to update foreign keys in single one statement - sql

Question

I want to update foreign keys into a table named User where foreign keys refer to a Project table, a Group table.
The user belongs to a project, within a group, the group are defined to the project level. The detailed user information are also stored into a table ToolUser
The create statement for the User table is as following:
CREATE TABLE [dbo].[User](
[ID] [int] IDENTITY(1,1) NOT NULL,
[IDproject] [int] NOT NULL,
[IDtoolUser] [int] NOT NULL,
[IDgroup] [int] NOT NULL,
[datemodified] [datetime] NOT NULL DEFAULT (getdate())
IDproject is FK for ID in Project table
IDtoolUser is FK for ID in ToolUser table
IDgroup is FK for ID in Group table
The update I want to perform consist in changing the group the user is assigned to which requires to resolve the project ID, the group ID before updating the groupID in the User table
I came up with a solution where the group id is calculed with a function, [dbo].[IDofGroup], and used into an UPDATE statement as following
UPDATE [dbo].[User]
SET IDgroup = [dbo].[IDofGroup]('TESTPROJ','none')
FROM [dbo].[User] as u
INNER JOIN [dbo].[Group] g
ON g.[ID]= u.[IDgroup]
INNER JOIN [dbo].[Project] p
ON p.[ID]= u.[IDproject]
AND p.[name] ='TESTPROJ'
WHERE g.[name] = 'TESTGROUP'
GO
The function IDofGroup itself performs couple SELECT to resolve project ID and group ID as following
ALTER FUNCTION [dbo].[IDofGroup]
(
-- Add the parameters for the function here
#ProjectName as varchar(max),
#GroupName as varchar(max)
)
RETURNS int
AS
BEGIN
-- Declare the return variable here
DECLARE #ProjectID int, #ResultID int
SET #ResultID=0
-- get project ID for #ProjectName
SELECT #ProjectID= ID
FROM [dbo].[Project]
WHERE [name]=#ProjectName
-- find id fro group which name is #GroupName and project ID #ProjectID
SELECT #ResultID= ID
FROM [dbo].[Group]
WHERE [IDproject]=#ProjectID
AND [name]=#GroupName
-- Return the result of the function
RETURN #ResultID
END
I m wondering if there any way to perform the UPDATE with some kind of JOIN in a single UPDATE statement w/o the need of using of function IDofGroup or other SELECT statements before the UPDATE statement

Answer 1

Try this one:
UPDATE u
SET IDgroup = g1.[ID]
FROM [dbo].[User] as u
INNER JOIN [dbo].[Project] p
ON p.[ID]= u.[IDproject]
INNER JOIN [dbo].[Group] g
ON g.[ID]= u.[IDgroup]
INNER JOIN [dbo].[Group] g1
ON g.[IDproject] = g1.[IDproject]
WHERE p.[name] ='TESTPROJ'
AND g.[name] = 'TESTGROUP'
AND g1.[name] = 'none'