Question about creating an SQL search

Question

Hi, In the app I am developing the user can search one of my database tables by one or more of three fields. If a field is left blank is there anyway to set up an SQL statement so that a dummy search criteria is entered for that field? That probably isn't very clear, here example:
I have 3 fields: ID, Surname and Forname. Currently in my app code I am checking whether fields are empty, or if two are empty and one isn't etc, before constructing the appropriate SQL statement with the fields that are not empty. What I am after is something like this, so I can just have one SQL statement that can handle one or more of the fields being empty, for example if the ID and Forname search fields have something in them, but the Surname field is empty:
Select * from employees where ID = 2 AND Surname = 'ANY' AND Forname = 'Smith'
Thanks

Answer 1

Ushitaki,
Yes, that's a good point you are raising here. The NVL always evaluates both expressions and results in a full table scan.
However, your variant might be "evil" as well since you are also using one query to handle two situations: one where you'd want a index scan because a value was given and one where you'd want a full table scan because the user did not provide a value.
So if performance is a problem here, the best option probably is to dynamically construct the query, using binds, but have several different queries populating the library cache, each with its own optimal plan.
Regards,
Rob.
Here are some results from my test:
SQL> create table mytable
  2  as
  3  select l id, '*********' description from (select level l from dual connect by level <= 10000)
  4  /
Tabel is aangemaakt.
SQL> create index i1 on mytable(id)
  2  /
Index is aangemaakt.
SQL> exec dbms_stats.gather_table_stats(user,'MYTABLE',cascade=>true)
PL/SQL-procedure is geslaagd.
SQL> alter session set sql_trace true
  2  /
Sessie is gewijzigd.
SQL> declare
  2    cursor c1(b_id number) is select id,description from mytable where id = nvl(b_id,id);
  3    cursor c2(b_id number) is select id,description from mytable where id = b_id or b_id is null;
  4  begin
  5    for r in c1(1) loop null; end loop;
  6    for r in c1(null) loop null; end loop;
  7    for r in c2(1) loop null; end loop;
  8    for r in c2(null) loop null; end loop;
  9  end;
10  /
PL/SQL-procedure is geslaagd.
SQL> disconnectAnd tkprof shows:
SELECT ID,DESCRIPTION
FROM
MYTABLE WHERE ID = NVL(:B1 ,ID)
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.00       0.00          0          0          0           0
Execute      2      0.09       0.14          0          0          0           0
Fetch    10003      0.32       0.34          0      10007          0       10001
total    10006      0.41       0.48          0      10007          0       10001
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 9833     (recursive depth: 1)
Rows     Row Source Operation
  10001  CONCATENATION
  10000   FILTER
  10000    TABLE ACCESS FULL MYTABLE
      1   FILTER
      1    TABLE ACCESS BY INDEX ROWID MYTABLE
      1     INDEX RANGE SCAN I1 (object id 2674783)
SELECT ID,DESCRIPTION
FROM
MYTABLE WHERE ID = :B1 OR :B1 IS NULL
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.00       0.00          0          0          0           0
Execute      2      0.24       0.33          0          0          0           0
Fetch    10003      0.22       0.31          0      10034          0       10001
total    10006      0.46       0.65          0      10034          0       10001
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 9833     (recursive depth: 1)
Rows     Row Source Operation
  10001  TABLE ACCESS FULL MYTABLE
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