How not to bring a particular column in SQL using IF and ELSE?

Question

Gentlemen, I have a table where I want to bring the column when the value is null but when it is filled it should not be displayed, as I can implement this condition in SQL ?

SELECT 
    OBS.NUOBS,
    OBS.DTOBS,
    OBS.CODUSU,
    OBS.OBS,
    OBS.PENDENTELOG,
    OBS.DTHSOBS,
    OBS.REGINC,
    OBS.DHPROXCONTATO,
    OBS.ID,
    OBS.FIMATT

FROM AD_PRONTUARIOOBS OBS

LEFT JOIN AD_PRONTUARIOATT ATT (NOLOCK) ON ATT.PEDIDOEXTERNO = OBS.PEDIDOEXTERNO

Today I am developing the above query, column B would refer to table AD_PRONTUARIOATT

Answer 1

Using the CASE:

SELECT 
(CASE WHEN A.campo1 IS NULL THEN B.campo1 ELSE A.campo1 END) as Resultado
FROM tabelaA A
LEFT JOIN tabelaB B ON B.id = A.idB

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You can also use IIF, as said by @Robertodecampos

SELECT 
IIF(A.campo1 IS NULL, B.campo1, A.campo1) as Resultado
FROM tabelaA A
LEFT JOIN tabelaB B ON B.id = A.idB