count(*) and count(1)

What is the difference between count(1) and count(*) in a sql query
eg.
select count(1) from emp;
and
select count(*) from emp;

Nothing, they are the same, incur the same amount of work -- do the same thing,
take the same amount of resources.You can see this via:

ops$tkyte@ORA817.US.ORACLE.COM> alter session set sql_trace=true;

Session altered.

ops$tkyte@ORA817.US.ORACLE.COM> select count(*) from all_objects;

COUNT(*)
----------
27044

ops$tkyte@ORA817.US.ORACLE.COM> select count(1) from all_objects
2 /

COUNT(1)
----------
27044


and the tkprof will show:



select count(*)
from
all_objects


call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.02 0.02 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 5.56 5.56 0 234998 4 1
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 5.58 5.58 0 234998 4 1

select count(1)
from
all_objects


call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.02 0.02 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 5.46 5.47 0 234998 4 1
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 5.48 5.49 0 234998 4 1

Same number of blocks read/written/processed, same cpu times (basically) same
elapsed times (basically).

they are identical.