Esto es lo que me quedó.
Select
case
when (t0.salunitmsr='PIEZA') then
($[rdr1.quantity] * t0.SWeight1)
when (t0.salunitmsr='kilo') then
($[rdr1.quantity])
when (t0.salunitmsr='caja') Then
($[rdr1.quantity] * t0.SWeight1)
when (t0.salunitmsr='rollo') then
($[rdr1.quantity] * t0.SWeight1)
when (t0.salunitmsr='saco') then
($[rdr1.quantity]*t0.sweight1)
When (t0.salunitmsr=tonelada)
($[rdr1.quantity])
end
From OITM T0
Where t0.itemcode=$[$38.1.11]
Gracias.