Determine the size of a SQL result set in KB

Question

I am hoping to find how I can get the kb size of a result set in OracleDB. I am not an sysadmin, but often run queries that return over 100k rows and I would need to find a

Answer 1

In SQL*Plus:

SET AUTOTRACE ON

SELECT *
FROM emp
WHERE rownum <= 100;

        27  recursive calls
         0  db block gets
        19  consistent gets
         4  physical reads
         0  redo size
     **11451  bytes sent via SQL*Net to client**
       314  bytes received via SQL*Net from client
         8  SQL*Net roundtrips to/from client
         0  sorts (memory)
         0  sorts (disk)
       100  rows processed

To use AUTOTRACE requires the PLUSTRACE role, which is not granted by default. Find out more.

Answer 2

Generally, you would replace your column list with a count(*) to return the row count.

I'm not sure how well that would work on really complicated queries with many joins and such but, for simpler queries, it should be fine. Replace:

select a,b,c from t where a > 7;

with

select count(*) from t where a > 7;

That will give you the row count before you run the real query. Just keep in mind there's a chance the data may change between your count query and real query (hopefully not too much). Knowledge of the data properties will allow you to approximate kilobytes from row count.