Oracle 系统函数 如何查表记录所占空间大小

how to search one table's size in Oracle:

--detail information

select * from dba_extents t where
LOWER(segment_name)='t_mnt_form_record'  and lower(t.owner)='test_usr' ;

--block count
select count(distinct substr(rowid,1,15)) from t_mnt_form_record

--one block 1 M size

[备注]以后再补充