Identify a table with maximum rows in Oracle

Question

I have a set of tables in Oracle and I would like to identify the table that contains the maximum number of rows.

So if, A has 200 rows, B has 345 rows and C has 120

Answer 1

David Aldridge correctly points out that querying all_tables could give incorrect results due to missing or stale table statistics. But there is also a problem with using user_segments; Deleted blocks beneath the high water mark would still be counted for the size of the table.

Example:

SQL>create table t as select * from all_objects

Table created.

SQL>select blocks, bytes from user_segments where segment_name = 'T';

    BLOCKS      BYTES
---------- ----------
       768    6291456

SQL>delete from t

52676 rows deleted.

SQL>commit;

Commit complete.

SQL>select count(*) from t;

  COUNT(*)
----------
         0

SQL>select blocks, bytes from user_segments where segment_name = 'T';

    BLOCKS      BYTES
---------- ----------
       768    6291456

SQL>truncate table t;

Table truncated.

SQL>select blocks, bytes from user_segments where segment_name = 'T';

    BLOCKS      BYTES
---------- ----------
         8      65536