Why index has bigger size than its table
I have a table with 25 columns, but most of the columns are null except the primary key. From dba_tables and dba_indexes, I worked out that the primary key index has 309 MB and the table has 280 MB.
Assume that index blocks contains the index key and table rowid, and table blocks contains its column data and the rowid. If this is true, the primary key index should has the same size as the table that is all null except the primary key. How come my index is 10% larger than the table?