Doing not change in due date when import the text file

Q：How should I do that the import was done once so as not to accept the import of the second times at the import of the text file? For example, how to do to not accept the changing in due date or changing in quantity at the order table?

A：

Display the Record Merge Rule dialog from the property "Record merge rule" in the Import tab in the data IO table.For each cell where "Added", "Modified", "Deleted", or "None" of the Internal Modification Flag and the External Modification Flag cross, select "Internal" from the dropdown list.Select cells and select "Internal" from the popup menu that can be displayed by right-clicking, the selected cells will change at once.
see the details from the help "Record Merge Rule dialog"(HelpNo:734500)

Next,click the field on the right side of the field mapping window(I/O), select "Internal preferred" from the dropdown list of "the property merge rule" at the "General" tab of the property window.
Now the setting is over. "Internal"and "Internal preferred" are confusing .
"Internal" means do not import.
"Internal preferred" means import when internal data does not exist.
see the details from the help "Merge rule and status flag "(HelpNo:757140)

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