UPDATE SQL with FROM and JOIN Statements

Hi Experts

The SQL Below is from SQL SErver. Following that is my attempt at an Oracle equivalent - but it is not working

      UPDATE AQD.qa_CheckList_Item SET Column1 = Standard_Item_GUID
      FROM AQD.qa_CheckList_Item CI
      INNER JOIN AQD.qa_StandardItem SI ON CI.column1 = SI.Standard_Item_ID
      INNER JOIN AQD.qa_Checklist_Properties CP ON CI.CheckList_Code = CP.CheckList_Code
      WHERE (CP.ColumnID = 1)
        AND (ISNUMERIC(CI.Column1) = 1)    -- Identities only
        AND (CP.Source IS NOT NULL)        -- we have a Standard
        AND (SI.[Standard] = CP.Source)    -- Standard must match

And in Oracle

UPDATE QA_CHECKLIST_ITEM
SET QA_CHECKLIST_ITEM.COLUMN1 = (SELECT DISTINCT CAST(sys.utl_raw.Cast_To_Varchar2(Standard_Item_GUID) AS Varchar2(38))
FROM AQD.QA_STANDARDITEM_SOURCE SI
INNER JOIN AQD.QA_CHECKLIST_ITEM CI ON CI.COLUMN1 = SI.STANDARD_ITEM_ID
INNER JOIN AQD.QA_CHECKLIST_PROPERTIES CP ON CI.CHECKLIST_CODE = CP.CHECKLIST_CODE
WHERE (CP.COLUMNID = 1)
  AND LENGTH(TRIM(TRANSLATE(CI.COLUMN1,' +.01234656789',' ')))IS NULL
  AND CP.SOURCE IS NOT NULL
  AND SI.STANDARD = CP.SOURCE
  AND rownum = 1);