SQL错误：无效数字：无效数字字符串

Question

在我的计算视图中具有以下逻辑，该逻辑引发错误。

 var_out = select  'PO' || cast('_' as varchar) || WERKS ||
                    cast('_' as varchar) || matnr + 
                    cast('_' as varchar) || ebeln as 
                    "EBELN",
                    menge as "Quantity"
                    from "ECC".EKPO;

EBELN字段的数据类型为VARCHAR100。您能在这里帮助我识别数据类型错误吗？