what's the difference between synonym and view? If i want to access in DATABASE A table AA from DATABASE B, i use create synonym AA for databasea@servera:AA, or use create a view with the same name AA on Database B, for accessing table AA in databaseA, is there any diffrence on result ? performance difference?

synonyms and views are different things.

Synonym references a table in the different database and the view is a combo of data from different tables combined into one.

Take a look at the manual.

YES! THANK YOU!! I forgot the basic for the view .