ORA-02022 remote statement has unoptimized view with remote object sqlserver merge command issue

This kind of statement is not supported by the Database Gateway.
Please review the Gateway documentation (http://docs.oracle.com/database/121/GMSWN/ch3.htm#GMSWN200) :
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Callback Support
SQL statements that require the gateway to callback to Oracle database would not be supported.

The following categories of SQL statements will result in a callback:

Any DML with a sub-select, which refers to a table in Oracle database. For example:
INSERT INTO emp@non_oracle SELECT * FROM oracle_emp;



ORA-02022 remote statement has unoptimized view with remote object

following is not supported in oracle
insert into tblDematDetails@Lnk_Datum (Oowncode) select Clientocode from demat where vallan=2015062 and compcode=17140
;