次のテーブルがあると仮定します。
create table Employee
(
ID VARCHAR2(4 BYTE) NOT NULL,
First_Name VARCHAR2(10 BYTE),
Last_Name VARCHAR2(10 BYTE),
Start_Date DATE,
End_Date DATE,
Salary Number(8,2),
City VARCHAR2(10 BYTE),
Description VARCHAR2(15 BYTE)
)
;
insert into employee (
ID, First_Name, Last_Name, Start_Date,
End_Date, Salary, City, Description)
select 21 + (level * 2) - 1,'Jason', 'Martin', to_date('19960725','YYYYMMDD'),
to_date ('20060725','YYYYMMDD'), 1234.56+level/3*5, 'Toronto', 'Programmer'
from dual
connect by level < 2501
;
次のクエリを実行しようとしているとき:
with tt2 as (
select t.*,
case when rownum = 1 then 1 when rownum = 3 then 3 else null end rfn
-- RFN は、必要な行にのみ番号を割り当てる複雑なケースの例です。直さないでください
from (select id, first_name, salary from employee) t
)
select
(select id from tt2 where rfn = 3) w
from dual
rfn = 3 (26 の 2500 行) の ID に似たすべての ID が返されます。
そして、ここに説明計画があります
"PLAN_TABLE_OUTPUT"
"Plan hash value: 2716438026"
" "
"--------------------------------------------------------------------------------------------------------"
"| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |"
"--------------------------------------------------------------------------------------------------------"
"| 0 | SELECT STATEMENT | | 2500 | | 12 (0)| 00:00:01 |"
"|* 1 | VIEW | | 2500 | 42500 | 4 (0)| 00:00:01 |"
"| 2 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6645_8CDDE2 | 2500 | 60000 | 4 (0)| 00:00:01 |"
"| 3 | TEMP TABLE TRANSFORMATION | | | | | |"
"| 4 | LOAD AS SELECT | SYS_TEMP_0FD9D6645_8CDDE2 | | | | |"
"| 5 | COUNT | | | | | |"
"| 6 | TABLE ACCESS FULL | EMPLOYEE | 2500 | 60000 | 8 (0)| 00:00:01 |"
"| 7 | VIEW | | 2500 | | 4 (0)| 00:00:01 |"
"| 8 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6645_8CDDE2 | 2500 | 60000 | 4 (0)| 00:00:01 |"
"--------------------------------------------------------------------------------------------------------"
" "
"Predicate Information (identified by operation id):"
"---------------------------------------------------"
" "
" 1 - filter(""RFN""=3)"
" "
"Note"
"-----"
" - dynamic sampling used for this statement (level=2)"
- 編集 -
たとえば、WITHにテーブルがあります：
「ID」「FIRST_NAME」「SALARY」「RFN」 "22" "ジェイソン" 1236.23 1 "24" "ジェイソン" 1237.89 "26" "ジェイソン" 1239.56 3
RFN = 1 の給与を選択して、単一の番号 1236.23 を取得したい
しかし、同じクエリで、RFN = 3 の enyone の Salary を選択して、単一の番号 1239.56 を得たいと考えています。
等々。
しかし。このクエリごとに、N 行の FULL_TABLE_SCAN が作成されます。
with tt2 as (
select t.*, case when rownum = 1 then 1 when rownum = 3 then 3 else null end rfn
from (select id, first_name, salary from employee) t
)
select
(select salary from tt2 where rfn = 1) w,
(select salary from tt2 where rfn = 3) w
from dual
説明表:
('Plan hash value: 1823688231');
(' ');
('--------------------------------------------------------------------------------------------------------');
('| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |');
('--------------------------------------------------------------------------------------------------------');
('| 0 | SELECT STATEMENT | | 2500 | | 12 (0)| 00:00:01 |');
('|* 1 | VIEW | | 2500 | 40000 | 4 (0)| 00:00:01 |');
('| 2 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6651_8CDDE2 | 2500 | 60000 | 4 (0)| 00:00:01 |');
('|* 3 | VIEW | | 2500 | 40000 | 4 (0)| 00:00:01 |');
('| 4 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6651_8CDDE2 | 2500 | 60000 | 4 (0)| 00:00:01 |');
('| 5 | TEMP TABLE TRANSFORMATION | | | | | |');
('| 6 | LOAD AS SELECT | SYS_TEMP_0FD9D6651_8CDDE2 | | | | |');
('| 7 | COUNT | | | | | |');
('| 8 | TABLE ACCESS FULL | EMPLOYEE | 2500 | 60000 | 8 (0)| 00:00:01 |');
('| 9 | VIEW | | 2500 | | 4 (0)| 00:00:01 |');
('| 10 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6651_8CDDE2 | 2500 | 60000 | 4 (0)| 00:00:01 |');
('--------------------------------------------------------------------------------------------------------');
(' ');
('Predicate Information (identified by operation id):');
('---------------------------------------------------');
(' ');
(' 1 - filter("RFN"=1)');
(' 3 - filter("RFN"=3)');
(' ');
('Note');
('-----');
(' - dynamic sampling used for this statement (level=2)');
-- より明確にするために編集 --
からの期待される結果:
「ID」「FIRST_NAME」「SALARY」「RFN」 "22" "ジェイソン" 1236.23 1 "24" "ジェイソン" 1237.89 "26" "ジェイソン" 1239.56 3 "26" "ジャック" 1249.56 6 「26」 「ウィキ」 119.56 8
給与 給与1 給与2 名前 name2 1236.23 1249.56 119.56 ウィキジャック
~次のステートメントから:
with tt2 as (
select t.*, case when row_number() over (order by id) = 1 then 1 when row_number() over (order by id) = 3 then 3 else null end rfn
from (select id, first_name, salary from employee) t
)
select
(select salary from tt2 where rfn = 1) salary,
(select salary from tt2 where rfn = 6) salary1,
(select salary from tt2 where rfn = 8) salary2,
(select first_name from tt2 where rfn = 8) name,
(select first_name from tt2 where rfn = 6) name2
from dual
2500 行の 5 回のフル テーブル スキャンなし