SQL Server 2019

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DECLARE 
    @FirstName VARCHAR(MAX),
    @LastName VARCHAR(MAX),
    @Email VARCHAR(MAX),
    @Mobile  VARCHAR(MAX),
    
    @FirstName_prev VARCHAR(MAX),
    @LastName_prev VARCHAR(MAX),
    @Email_prev VARCHAR(MAX),
    @Mobile_prev  VARCHAR(MAX),
    
    @loop_start  INT = 0;
    
DECLARE @tmp TABLE(
    FirstName VARCHAR(MAX),
    LastName VARCHAR(MAX),
    Email VARCHAR(MAX),
    Mobile  VARCHAR(MAX)
);

DECLARE cursor_Contacts CURSOR
FOR SELECT FirstName,LastName,Email,Mobile
    FROM (
    
    SELECT 1 id, 'a' FirstName,'b' LastName,NULL Email,NULL Mobile,NULL Notes UNION ALL
    SELECT 2, 'a','b',NULL,NULL,NULL UNION ALL
    SELECT 7, 'a','b','d','e',NULL UNION ALL
    SELECT 8, 'a','b','d',NULL,NULL UNION ALL
    SELECT 3, 'aa',NULL,'cc',NULL,NULL UNION ALL
    SELECT 4, 'aa',NULL,NULL,NULL,NULL UNION ALL
    SELECT 5, NULL,'bbb',NULL,NULL,NULL UNION ALL
    SELECT 6, NULL,'bbb',NULL,NULL,NULL
    
    )Contacts
    ORDER BY ISNULL(FirstName,'ZZZZZZZZZZZZZZZ')
    ,ISNULL(LastName,'ZZZZZZZZZZZZZZZ')
    ,ISNULL(Email,'ZZZZZZZZZZZZZZZ')
    ,ISNULL(Mobile,'ZZZZZZZZZZZZZZZ');
 
OPEN cursor_Contacts;
 
FETCH NEXT FROM cursor_Contacts INTO 
     @FirstName,@LastName,@Email,@Mobile;
 
WHILE @@FETCH_STATUS = 0
    BEGIN
    
        --SELECt @FirstName,@LastName,@Email,@Mobile;
    
        IF @loop_start = 0
        
        BEGIN
        
            INSERT INTO @tmp(FirstName,LastName,Email,Mobile)
            VALUES (@FirstName,@LastName,@Email,@Mobile)
            
            SET @loop_start = 1
        
        END
        
        ELSE
        BEGIN
        
            IF
            (@FirstName_prev = @FirstName OR @FirstName IS NULL) AND
            (@LastName_prev = @LastName OR @LastName IS NULL) AND
            (@Email_prev = @Email OR @Email IS NULL) AND
            (@Mobile_prev = @Mobile OR @Mobile IS NULL)
            
            BEGIN
                SET @loop_start = 1
            END
            
            ELSE
            BEGIN
                SET @loop_start = 2
                
                INSERT INTO @tmp(FirstName,LastName,Email,Mobile)
                VALUES (@FirstName,@LastName,@Email,@Mobile)
            END
        END;
        
        
        SET @FirstName_prev = @FirstName
        SET @LastName_prev= @LastName
        SET @Email_prev = @Email
        SET @Mobile_prev= @Mobile;
        
        
        FETCH NEXT FROM cursor_Contacts INTO 
            @FirstName,@LastName,@Email,@Mobile;
    END;
 
CLOSE cursor_Contacts;

SELECT * FROM @tmp;
 
DEALLOCATE cursor_Contacts;

FirstName	LastName	Email	Mobile
a	b	d	e
aa	null	cc	null
null	bbb	null	null