看看这种错误消息的一个例子：
combination reference table/field XXX does not exist
引起错误的字段类型为LOSMENGE，字段名为INSLO:
该字段的基本数据类型(Data Type)为 QUAN，长度为13.
根据ABAP帮助文档, QUAN类型需要和某种单位字段结合在一起，用于描述实际业务流程中的数量，比如 一本书，一件啤酒，一捆绳子等等。
A quantity field is a component of a structure, database table, or view of type QUAN defined in ABAP Dictionary, used to include a quantity in a specific unit. A quantity field must be associated with a unit key of a structure, database table, or view which determines the unit and the number of fractional digits. A unit key is a component of a structure, database table, or view of type UNIT defined in ABAP Dictionary and can contain a unit ID from the database table T006.
按照ABAP帮助文档里的规定，类型为QUAN的字段，必须设置一个类型为 UNIT 的字段作为单位，二者共同描述“数量”这个概念，缺少单位，数量单位的语义就不完整。
A data element of data type QUAN is handled as a field of data type DEC and is stored in database tables in the BCD format. When creating a data element or a structure component of the data type QUAN in the ABAP Dictionary tool, any number of fractional digits can be defined. The default value is no fractional digits.
For every structure component of data type QUAN, a component of the same structure or of a different structure, database table, or view must be specified in the individual editing of the component as a reference field, which has the data type UNIT. This field is the unit key which determines the unit of the quantity. From a technical perspective, the data type UNIT is handled like a type CHAR with length 2.
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