USE tempdb;
GO

CREATE TABLE #TempTab
(
    TaId int IDENTITY(1, 1) NOT NULL PRIMARY KEY CLUSTERED,
    TaNote varchar(200),
    TaNum int
);
GO

INSERT INTO #TempTab (TaNote, TaNum)
VALUES 
    ('', NULL),
    ('', 0),
    ('', 30),
    ('', 54),
    ('', 60),
    ('', 90),
    ('', 1800),
    ('', 3600),
    ('', 3630),
    ('', 5400),
    ('', 5430)
    ;
GO

-- DECLARE @NomeEccetera int = 4;
-- nela applicazione non posso usare DECLAIRE !!!

SELECT 
    TaId, 
    TaNote, 
    TaNum, 
    CASE WHEN ISNULL(CONVERT(Varchar, TaNum), '') = '' THEN 'n' ELSE (CONVERT(Varchar, CONVERT(INT, TaNum / 3600)) + 'h ' + CONVERT(Varchar, CONVERT(FLOAT, TaNum - CONVERT(INT, TaNum / 3600) * 3600) / 60) + 'm') END AS Risultato
FROM
    #TempTab
;

DROP TABLE #TempTab;
GO