不为空时从其他表更新表日期字段

Question

我想从同一表中的某些记录（条目类型= 1）更新表中条目类型= 4的日期，但是无法将空数据插入字段错误。

UPDATE [Item Ledger Entry] 
  SET [Last Invoice Date] = (Select  MAX([Posting Date])
                               from  [Item Ledger Entry] ILE2 
                               where ILE2.[Item No_] = ILE1.[Item No_] AND
                                     ILE2.[Posting Date] <= ILE1.[Posting Date] AND
                                     ILE2.[Entry Type] = 1 AND 
                                     ILE2.[Posting Date] is not null
                            )
 FROM  [Item Ledger Entry] ILE1
 where ILE1.[Entry Type] = 4