connect from Oracle to MS SQL and execute Oracle query from Oracle to SQL server

both

A gateway is required to connect Oracle to SQL Server - this is where you define the drivers to  Oracle so it knows how to "speak" to sql server

The query will then execute across a database link that runs via the gateway

ststuber, I'm surprised you didn't link to your most excellent article for marrowyung :)

A full how to on how to set it up is in this article:
https://www.experts-exchange.com/Database/Oracle/A_9850-Configuring-and-using-Oracle-Database-Gateway-for-ODBC.html

"Also, while the ODBC gateway should work, it is better to use the SQL Server specific gateway provided you have a license for it."

yeah, It need a license, thanks for that.

so only oracle gateway can do ? any thing like Database link ? what is the different between the gateway and link ?

The ODBC gateway (the generic gateway) is free - no license required.

A database link is an Oracle construct that allows Oracle to talk to another database.  It can talk Oracle to Oracle natively.

The Gateway is the set of protocols that allows the Oracle database - via a database link to talk to a non Oracle database.  The generic gateway allows you to set up a connection to any ODBC compliant database.  Follow the instructions in the article and it should work just fine for you.

"A database link is an Oracle construct that allows Oracle to talk to another database.  It can talk Oracle to Oracle natively."

only Oracle to Oracle ?

so Oracle Gateway to all OTHER vendor's DB I think, right?

ok, thanks.