For a start, check other similar posts on GeoNet:
connect oracle 12c from arcgis for desktop and server 10.3.1
hi Asrujit SenGupta,
im using 10.5, 12C R2(12.2) on the same machine, and even i can connect to sqlplus from CMD
Oracle database requirements for ArcGIS 10.5.x—System Requirements | ArcGIS Desktop
*You must install ArcGIS 10.5.1 (Desktop, Engine, Server) Oracle critical issues and 12.2.01 Support Patch on all 10.5.1 client machines to use Oracle 12.2.01 with ArcGIS
I think connection from ArcGIS Desktop 10.5 is not supported. You will need Desktop 10.5.1 along with the below patch:
ArcGIS 10.5.1 (Desktop, Engine, Server) Oracle critical issues and 188.8.131.52 support Patch
Also, make sure you are putting the correct hostname in the connection file.
any idea abt this ???
You must have ArcGIS 10.5 installed.....the patch is for ArcGIS 10.5.1. Desktop 10.5 and Desktop 10.5.1 are different ArcGIS Desktop versions.
So download the setup for ArcGIS Desktop 10.5.1, install it, install the patch and then try connecting to your Database.
Is it the same patch for 10.6.1?
ArcMap or ArcGIS 10.6.1 supports Oracle 12.2 and here is the web help link:
Oracle database requirements for ArcGIS 10.6.x—System Requirements | ArcGIS Desktop
Asrujit suggested the oracle critical patch for ArcMAP 10.5.1 as you are using 10.5.1 with Oracle 12.2. If you upgraded your ArcGIS Desktop or AraMAP to 10.6.1 then you can directly connect to Oracle 12.2 as 10.6.1 supports Oracle 12.2 and do not need the patch. That patch is for ArcMAP 10.5.1.
Database is still 11G and has no SDE. I have no issues to connect to the database from 10.2.2 desktop. We are testing upgrade to 10.6.1 now.
10.6.1 supports both oracle 11g ( Oracle 184.108.40.206) and Oracle 12.2. You should be good to go as far as connection from ArcGIS is concern.