Strange as it may sound, in this specific case two combined cross joins can help.
Look at the below example.
Sample data table:
select * from all_tables;
drop table Purchases;
create table Purchases as
select zx.object_id + (lev-1) * 100000 purchase_id,
object_name purchase_name,
round( dbms_random.value( 1, 200 )) purchase_price,
zx.*
from all_objects zx
cross join (select level lev from dual connect by level <= 170);
create unique index purchases_id_ix on Purchases( Purchase_id );
exec dbms_stats.gather_table_stats( user, 'Purchases' );
select count(*) from Purchases;
COUNT(*)
----------
10316620
The query:
var Purchase_id varchar2( 4000 )
var Purchase_name varchar2( 4000 )
var Purchase_price varchar2( 4000 )
begin
:Purchase_id := '1139';
:Purchase_name := NULL;
:Purchase_price := NULL;
end;
/
explain plan for
select p.*
from Purchases p
cross join (
select 1 from dual d
where :Purchase_id is not null
) part_1
where Purchase_id = to_number( :Purchase_id )
and ( :Purchase_name is null or Purchase_name = :Purchase_name )
and ( :Purchase_price is null or purchase_price = to_number( :Purchase_price ) )
union all
select p.*
from Purchases p
cross join (
select 1 from dual d
where :Purchase_id is null
) part_2
where
( :Purchase_name is null or Purchase_name = :Purchase_name )
and ( :Purchase_price is null or purchase_price = to_number( :Purchase_price ) )
;
The explain plan:
Plan hash value: 460094106
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 28259 | 5546K| 54093 (1)| 00:10:50 |
| 1 | NESTED LOOPS | | 28259 | 5546K| 54093 (1)| 00:10:50 |
| 2 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
| 3 | VIEW | VW_JF_SET$96C1679A | 28259 | 5546K| 54091 (1)| 00:10:50 |
| 4 | UNION-ALL | | | | | |
|* 5 | FILTER | | | | | |
|* 6 | TABLE ACCESS BY INDEX ROWID| PURCHASES | 1 | 132 | 3 (0)| 00:00:01 |
|* 7 | INDEX UNIQUE SCAN | PURCHASES_ID_IX | 1 | | 2 (0)| 00:00:01 |
|* 8 | FILTER | | | | | |
|* 9 | TABLE ACCESS FULL | PURCHASES | 28258 | 3642K| 54088 (1)| 00:10:50 |
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - filter(:PURCHASE_ID IS NOT NULL)
6 - filter((:PURCHASE_NAME IS NULL OR "P"."PURCHASE_NAME"=:PURCHASE_NAME) AND
(:PURCHASE_PRICE IS NULL OR "P"."PURCHASE_PRICE"=TO_NUMBER(:PURCHASE_PRICE)))
7 - access("P"."PURCHASE_ID"=TO_NUMBER(:PURCHASE_ID))
8 - filter(:PURCHASE_ID IS NULL)
9 - filter((:PURCHASE_NAME IS NULL OR "P"."PURCHASE_NAME"=:PURCHASE_NAME) AND
(:PURCHASE_PRICE IS NULL OR "P"."PURCHASE_PRICE"=TO_NUMBER(:PURCHASE_PRICE)))
27 wierszy zosta│o wybranych.
Test for :Purchase_id <> NULL
SQL> set pagesize 0
SQL> set linesize 200
SQL> set timing on
SQL> set autotrace traceonly
SQL>
SQL> begin
2 :Purchase_id := '163027';
3 :Purchase_name := NULL;
4 :Purchase_price := NULL;
5 end;
6 /
Procedura PL/SQL zosta│a zako˝czona pomyťlnie.
Ca│kowity: 00:00:00.00
SQL> select p.*
2 from Purchases p
3 cross join (
4 select 1 from dual d
5 where :Purchase_id is not null
6 ) part_1
7 where Purchase_id = to_number( :Purchase_id )
8 and ( :Purchase_name is null or Purchase_name = :Purchase_name )
9 and ( :Purchase_price is null or purchase_price = to_number( :Purchase_price ) )
10 union all
11 select p.*
12 from Purchases p
13 cross join (
14 select 1 from dual d
15 where :Purchase_id is null
16 ) part_2
17 where
18 ( :Purchase_name is null or Purchase_name = :Purchase_name )
19 and ( :Purchase_price is null or purchase_price = to_number( :Purchase_price ) )
20 ;
Ca│kowity: 00:00:00.09
Plan wykonywania
----------------------------------------------------------
Plan hash value: 460094106
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 28259 | 5546K| 54093 (1)| 00:10:50 |
| 1 | NESTED LOOPS | | 28259 | 5546K| 54093 (1)| 00:10:50 |
| 2 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
| 3 | VIEW | VW_JF_SET$96C1679A | 28259 | 5546K| 54091 (1)| 00:10:50 |
| 4 | UNION-ALL | | | | | |
|* 5 | FILTER | | | | | |
|* 6 | TABLE ACCESS BY INDEX ROWID| PURCHASES | 1 | 132 | 3 (0)| 00:00:01 |
|* 7 | INDEX UNIQUE SCAN | PURCHASES_ID_IX | 1 | | 2 (0)| 00:00:01 |
|* 8 | FILTER | | | | | |
|* 9 | TABLE ACCESS FULL | PURCHASES | 28258 | 3642K| 54088 (1)| 00:10:50 |
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - filter(:PURCHASE_ID IS NOT NULL)
6 - filter((:PURCHASE_NAME IS NULL OR "P"."PURCHASE_NAME"=:PURCHASE_NAME) AND
(:PURCHASE_PRICE IS NULL OR "P"."PURCHASE_PRICE"=TO_NUMBER(:PURCHASE_PRICE)))
7 - access("P"."PURCHASE_ID"=TO_NUMBER(:PURCHASE_ID))
8 - filter(:PURCHASE_ID IS NULL)
9 - filter((:PURCHASE_NAME IS NULL OR "P"."PURCHASE_NAME"=:PURCHASE_NAME) AND
(:PURCHASE_PRICE IS NULL OR "P"."PURCHASE_PRICE"=TO_NUMBER(:PURCHASE_PRICE)))
Statystyki
----------------------------------------------------------
1 recursive calls
0 db block gets
4 consistent gets
2 physical reads
0 redo size
1865 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
Test for :Purchase_id = NULL
SQL> begin
2 :Purchase_id := NULL;
3 :Purchase_name := 'DBMS_CUBE_UTIL';
4 :Purchase_price := NULL;
5 end;
6 /
Procedura PL/SQL zosta│a zako˝czona pomyťlnie.
Ca│kowity: 00:00:00.00
SQL> select p.*
2 from Purchases p
3 cross join (
4 select 1 from dual d
5 where :Purchase_id is not null
6 ) part_1
7 where Purchase_id = to_number( :Purchase_id )
8 and ( :Purchase_name is null or Purchase_name = :Purchase_name )
9 and ( :Purchase_price is null or purchase_price = to_number( :Purchase_price ) )
10 union all
11 select p.*
12 from Purchases p
13 cross join (
14 select 1 from dual d
15 where :Purchase_id is null
16 ) part_2
17 where
18 ( :Purchase_name is null or Purchase_name = :Purchase_name )
19 and ( :Purchase_price is null or purchase_price = to_number( :Purchase_price ) )
20 ;
510 wierszy zosta│o wybranych.
Ca│kowity: 00:00:11.90
Plan wykonywania
----------------------------------------------------------
Plan hash value: 460094106
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 28259 | 5546K| 54093 (1)| 00:10:50 |
| 1 | NESTED LOOPS | | 28259 | 5546K| 54093 (1)| 00:10:50 |
| 2 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
| 3 | VIEW | VW_JF_SET$96C1679A | 28259 | 5546K| 54091 (1)| 00:10:50 |
| 4 | UNION-ALL | | | | | |
|* 5 | FILTER | | | | | |
|* 6 | TABLE ACCESS BY INDEX ROWID| PURCHASES | 1 | 132 | 3 (0)| 00:00:01 |
|* 7 | INDEX UNIQUE SCAN | PURCHASES_ID_IX | 1 | | 2 (0)| 00:00:01 |
|* 8 | FILTER | | | | | |
|* 9 | TABLE ACCESS FULL | PURCHASES | 28258 | 3642K| 54088 (1)| 00:10:50 |
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - filter(:PURCHASE_ID IS NOT NULL)
6 - filter((:PURCHASE_NAME IS NULL OR "P"."PURCHASE_NAME"=:PURCHASE_NAME) AND
(:PURCHASE_PRICE IS NULL OR "P"."PURCHASE_PRICE"=TO_NUMBER(:PURCHASE_PRICE)))
7 - access("P"."PURCHASE_ID"=TO_NUMBER(:PURCHASE_ID))
8 - filter(:PURCHASE_ID IS NULL)
9 - filter((:PURCHASE_NAME IS NULL OR "P"."PURCHASE_NAME"=:PURCHASE_NAME) AND
(:PURCHASE_PRICE IS NULL OR "P"."PURCHASE_PRICE"=TO_NUMBER(:PURCHASE_PRICE)))
Statystyki
----------------------------------------------------------
0 recursive calls
0 db block gets
197993 consistent gets
82655 physical reads
0 redo size
16506 bytes sent via SQL*Net to client
882 bytes received via SQL*Net from client
35 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
510 rows processed
To know real execution times, do not look at plans, they tell lies, contain only estimates (how oracle thinks it would be). Look at rows with "Ca│kowity", it means "Total execution time" (I don't know how to change a codepage to english in sqlplus). Also look at "consistent gets", this is a number of logical consistent blocks that the query reads.
The first query (purchase_id <> null )
Ca│kowity: 00:00:00.09
4 consistent gets
2 physical reads
obviously it uses the index, the time is 90 ms
The second query (purchase_id = null )
Ca│kowity: 00:00:11.90
197993 consistent gets
82655 physical reads
this query does full table scan.