SQL Null set to Zero for adding

SELECT Column1, Column2, Column3+Column4 AS [Added Values]
FROM Table

SELECT Column1, Column2, IIF(ISNULL(Column3),0,Column3) + IIF(ISNULL(Column4),0,Column4) AS [Added Values]
FROM Table

SELECT Column1, Column2, ISNULL(Column3, 0) + ISNULL(Column4, 0) AS [Added Values]FROM Table

nz (column3, 0)

SELECT
   Column1,
   Column2,
   COALESCE(Column3, 0) + COALESCE(Column4, 0) AS [Added Values]
FROM Table

SELECT Column1, Column2, Nz(Column3, 0) + Nz(Column4, 0) AS [Added Values]
FROM Table