sqlplus into the database as sys or system and run the following dbms package. Make sure you replace "SCHEMA_NAME" and "TABLE_NAME".

>
begin

dbms_stats.gather_table_stats(
ownname=> 'SCHEMA_NAME',
tabname=> 'TABLE_NAME' ,
estimate_percent=> DBMS_STATS.AUTO_SAMPLE_SIZE,
cascade=> DBMS_STATS.AUTO_CASCADE,
degree=> null,
no_invalidate=> DBMS_STATS.AUTO_INVALIDATE,
granularity=> 'AUTO',
method_opt=> 'FOR ALL COLUMNS SIZE AUTO');

end;
/

==============================================

2. A quick command to gather statistics on a schema:

sqlplus into the database as sys or system and simply run the following command:

>
exec dbms_stats.gather_schema_stats('SCHEMA_NAME');