Access Methods
Oracle finds the data to read by using the following methods:
• Full Table Scan (FTS). Using this method the whole table is read.
• Index Lookup (unique & non-unique). Using this method, data is accessed by looking up key values in an index and returning rowids where a rowid uniquely identifies an individual row in a particular data block.
• Rowid. This is the quickest access method available. Oracle simply retrieves the block specified and extracts the rows it is interested in. Most frequently seen in explain plans as Table access by Rowid.