I used the arcGIS tool feature class to feature class to successfull merge two identical feature classes [one with partial data and the other resting on a database connection]. However when I attempt to do this with arcPY I get a ERROR 000258: layer already exists, failed to execute .

The call looks like this

arcpy.FeatureClassToFeatureClass_conversion("roads", C:\fullPathTo.sde, "roads")

Other enviromental varibles have been set accordingly, but I am looking for what the GUI tool does in this situation, an automatic merge, taking the left [local] data and meging it into the .sde.


1 Answer 1


Feature class to feature class doesn't merge, it overwrites if allowed, or will give an error if the feature class already exists. If able to overwrite you will lose any data in the feature class that is overwritten - it will not be in the end result.

You need to use either:

  1. The Merge tool to merge two feature classes together into a new feature class with a new name
  2. The Append tool to merge one into another existing feature class (which is what I think you want to do)
  • What if we want to overwrite using feature class? Merge creates duplicate fields when I attempt and Append creates a shp file as opposed to feature layers
    – Surreal
    Sep 30, 2016 at 11:03

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