DB Aggregate Locking

Question

Could someone explain how the DB handles record locking when an aggregate function is called? For instance:
select count(*)
into   v_count
from   x;
...Is there a lock maintained on table x for the duration of the transaction so no rows can be inserted or deleted?

Answer 1

Hi,
crottyan wrote:
Could someone explain how the DB handles record locking when an aggregate function is called? For instance:
select count(*)
into   v_count
from   x;
...Is there a lock maintained on table x for the duration of the transaction so no rows can be inserted or deleted?No, a query by itself never keeps anyone from changing the table. Whether or not the query uses an aggregate function doesn't change that.
The output you get will reflect the contents of the table at the time you started the query. That's called Read Consistency , and it's been a feature of Oracle since version 4.
Edited by: Frank Kulash on Jul 17, 2012 12:37 PM
You can use "SELECT ... *FOR UPDATE* " if you really want to keep other sessions from changing rows in your query, but the only reason for doing this is if you might change them yourself. You can't use FOR UPDATE and aggregate functions together.