원격에서 정보를 가져오는 부분에 있어서 제한이 있다.

그 제한을 알고 제대로 활용해보자.

Aggregate functions like MAX(), COUNT() are NOT passed across the net but rather are performed on the local node.

Expressions in the SELECT list are decomposed into columns and evaluated when the data is retrieved.

Only a relevant subset of columns are fetched across the net.

An expression in a WHERE clause is passed across to the remote database if it compares the remote column to a literal (eg ename = 'KING').

Expressions in a WHERE clause are passed to the remote database if all columns are in the expression are located in the same remote table the remote database (eg emp.sal * 0.20 > emp.bonus)

Datatype conversion functions like TO_CHAR() in a WHERE clause are subject to the conditions in #4 and #5.

The optimizer only has knowledge of local indexes when making decisions about how to execute a query.

Remote indexes can be still be used to resolve the decomposed query sent to the remote database.

GROUP BY is not sent to the remote database.

ORDER BY is not sent to the remote database.