Estimate Index Size in OraDB

We can use explain plan for Index create to estimate the size of an Index.

 
SQL> EXPLAIN PLAN FOR CREATE INDEX DB_OBJECT_IDX ON DB_OBJECT(COL_NAME);
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
...
PLAN_TABLE_OUTPUT
...

estimated index size: 159M bytes

But this does not give good enough estimates when majority values in the column are NULL.

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