How to Improve Performance of Query expression?

Your question is just scratching the surface of a very nuanced and deep topic.  The very first thing we'll need to know is if it's the amount that you're trying to query, or if it's the implementation of the Appian, or the implementation of that portion of the DB.

If you're querying from a table or a view, see how long it takes to get the same data from the RDBMS.  Chances are, if there's churn there, there will be slightly more when you get Appian involved.

We have to know how far upstream or downstream the problem is before we can help more.

Your question is just scratching the surface of a very nuanced and deep topic.  The very first thing we'll need to know is if it's the amount that you're trying to query, or if it's the implementation of the Appian, or the implementation of that portion of the DB.

If you're querying from a table or a view, see how long it takes to get the same data from the RDBMS.  Chances are, if there's churn there, there will be slightly more when you get Appian involved.

We have to know how far upstream or downstream the problem is before we can help more.