Failed to open table. Error: An Item with the same key has already been added

Question

I keep getting this error message when after joining a table with no spatial data to a Shapefile via a common attribute

I'm new to ArcGIS but have been able to do this easily using QGIS recently. I have literally no idea what the message means. This has happened with two separate shp files.

Can someone help please?

DanPatterson_Retired · Answer

Zoltan, my image shows the suffix behaviour… it was done in Pro

zkovacs · Answer

Unique field names were always a case when creating new tables/feature classes even in ArcMap. Joins are created with SQL statements and such, the resulting schema is always referred to with fully qualified field names - eg. sourcename.fieldname. Therefore it shouldn't matter if I have the same field name(s) in the table to be joined.

ArcMap is perfectly capable of dealing with this, and if the result is exported the field names are automatically suffixed as '_1', '_2' etc. to ensure the unique field naming. I'd expect the same behaviour in Pro...

DanPatterson_Retired · Answer

I think ArcGIS Pro is being a little more forward thinking in ensuring that requirements are being met

For geodatabase fields....

Define fields in tables—Geodatabases | ArcGIS Desktop

Field names in the same table must be unique; for instance, you can't have two columns with the name ObjectID. Field names must also start with a letter and not contain spaces or reserved words. Field names are limited to 64 characters for file geodatabases, 31 characters in SQL Server and SQLExpress, 30 characters in Oracle and DB2; dBASE is limited to 10 characters.

There is loads more information there.  The above defines the 'within' table situation.  When joining, the field names do become unique... ie a sample of using Join Field for two polygon featureclasses, keeping the geometry information