[mamcx]

Esto te pasa porque son 2 condiciones, no 1, sobre las que esta el pivot.

Código SQL [-]

SELECT 
    IDMuestra,
   max (case when IDLab = 1 and IDMuestra = 'Sample-01'  then TenorAu end) as Lab1,
   max (case when IDLab = 2 and IDMuestra = 'Sample-01'  then TenorAu end) as Lab2,
   max (case when IDLab = 3 and IDMuestra = 'Sample-01'  then TenorAu end) as Lab3
FROM 
(
    SELECT 'Sample-01'  IDMuestra, 4.5  TenorAu, 1 IDLab
    UNION ALL
    SELECT 'Sample-01', 6.5, 2
    UNION ALL
    SELECT 'Sample-01', 8, 3
)a
GROUP BY IDMuestra