IF OBJECT_ID(N'tempdb..#T1') IS NOT NULL 
    DROP TABLE #T1;
	
IF OBJECT_ID(N'tempdb..#T2') IS NOT NULL 
    DROP TABLE #T2;
	
CREATE TABLE #T1 (ID INT PRIMARY KEY);

CREATE TABLE #T2
    (T1ID INT NOT NULL,
     Col1 VARCHAR(10));

INSERT  INTO #T1
        (ID)
VALUES  (1),
        (2),
        (3),
        (4);

INSERT  INTO #T2
        (T1ID, Col1)
VALUES  (1, 'A'),
        (1, 'B'),
        (2, 'A'),
        (2, 'B'),
        (2, 'C'),
        (3, 'A');

SELECT  *
FROM    #T1;

SELECT  COUNT(*)
FROM    #T1;

SELECT  *
FROM    #T1
        INNER JOIN #T2
            ON #T1.ID = #T2.T1ID;

SELECT  COUNT(#T1.ID)
FROM    #T1
        INNER JOIN #T2
            ON #T1.ID = #T2.T1ID;