Hard Parse or Soft Parse ?

Question

Hi Experts,
If we execute a SELECT statement in SQL*PLUS by passing the value using ampersand operator, whether hard parsing will occur or soft parsing ?
SQL> select last_name from employees where department_id = &dept_no;
Enter value for dept_no: 100
old   1: select last_name from employees where department_id = &dept_no
new   1: select last_name from employees where department_id = 100
SQL> select last_name from employees where department_id = &dept_no;
Enter value for dept_no: 110
old   1: select last_name from employees where department_id = &dept_no
new   1: select last_name from employees where department_id = 110
When I am executing V$SQL, for each different value I am seeing different SQL_ID. Please explain on this.
Many thaks in advance for your help.
Cheers,
Suri

Answer 1

hi ,
the best way to check for for hard parse and soft parse is by querying the data dictionar view v$sqlarea . There is a column called parse_counts(not sure of the name). the moment you execute a query , a row is reflected in this view.
for eg , when you query
select * from emp where empno=101,
select * from emp where empno=102,
select * from emp where empno=103,
query the v$sqlarea  with a filter predicate on the sql_text . i.e  select * from v$sqlarea where sql_text like  '%select * from emp %'.
And then try querying the emp table using bind variable,
select * from emp where empno=:x; -- pass 101 ,102,103
No new rows are formed in the v$sqlarea,rather the parsed_count keeps on increasing , contrary to the above queries(without using bind variables in which each query is new to the parser).
@Gurus : in 11g , i  have observed that all queries are converted to make you of bind variables .I knew that this was the implicit behaviour of plsql ,but now have they enhanced the sql engine too ?
Thanks
Rahul