サブクエリとアクセスヒント句

• MySQL

(8.0.26)
-- 1. テストデータ作成

drop table tab1;
create table tab1(
    col1 bigint 
   ,col2 bigint
   );

drop table tab2;
create table tab2(
    col1 bigint 
   ,col2 bigint
   );

drop table tab3;
create table tab3(
    col1 bigint 
   ,col2 bigint
   );

drop procedure proc1;

delimiter //
create procedure proc1(in x int)
begin
  declare i int;
  set i = 0;
  start transaction;
  while i < x do
    set i = i + 1;
    insert into tab1 values(
     i
    ,floor(rand() * 100000)+1
    );
    insert into tab2 values(
     i
    ,floor(rand() * 100000)+1
    );
    insert into tab3 values(
     i
    ,floor(rand() * 100000)+1
    );
  end while;
  commit;
end
//
delimiter ;

call proc1(1000000);

select count(*) from tab1;
select * from tab1 order by rand() limit 20;
alter table tab1 add constraint tab1pk primary key (col1);
create index ind12 on tab1(col2);

select count(*) from tab2;
select * from tab2 order by rand() limit 20;
alter table tab2 add constraint tab2pk primary key (col1);
create index ind22 on tab2(col2);

select count(*) from tab3;
select * from tab3 order by rand() limit 20;
alter table tab3 add constraint tab3pk primary key (col1);
create index ind32 on tab3(col2);

analyze table tab1;
analyze table tab2;
analyze table tab3;

--2. 動作確認

explain
select  /* NO_INDEX(t6  ind22 ) */    count(*) from tab1 t1
where exists ( select 1 from
  (
   select /* QB_NAME(qb1) */  /* NO_INDEX(t21 ind22 ) */   t21.col2 from tab2 t21 inner join tab3 t22
   on t21.col1 = t22.col1
   where t21.col2 < 5000
   group by t21.col2
   having count(t22.col2) > 100
  ) t2 where t1.col2 = t2.col2 )
and exists ( select 1 from
  (
   select /* QB_NAME(qb2) */ /* NO_INDEX(t31 ind22 ) */  t31.col2 from tab2 t31 inner join tab3 t32
   on t31.col1 = t32.col1
  ) t3 where t1.col2 = t3.col2 )
and exists ( select /* QB_NAME(qb3) */ /* NO_INDEX(t4  ind12) */  1 from tab1 t4 where t1.col1 = t4.col2)
and exists ( select /* QB_NAME(qb4) */ /*+ NO_INDEX(t6  ind22 ) */   1 from tab1 t5 inner join tab2 t6 on t5.col1 = t6.col1 where t1.col1 = t5.col1 and t1.col2 = t6.col2)
;

show warnings;

-- 問合せブロック付きヒント

/*+ NO_INDEX(t21@qb1 ind22 ) */     → OK
/*+ NO_INDEX(t31@qb2 ind22 ) */     → OK
/*+ NO_INDEX(t4@qb3  ind12) */      → OK
/*+ NO_INDEX(t6@qb4  ind22 ) */     → OK

-- サブクエリ内部名を本体に指定

/*+ NO_INDEX(t21 ind22 ) */     → Unresolved
/*+ NO_INDEX(t31 ind22 ) */     → Unresolved
/*+ NO_INDEX(t4  ind12) */      → Unresolved
/*+ NO_INDEX(t6  ind22 ) */     → Unresolved

-- サブクエリ内部名をサブクエリに指定

/*+ NO_INDEX(t21 ind22 ) */     → OK
/*+ NO_INDEX(t31 ind22 ) */     → OK
/*+ NO_INDEX(t4  ind12) */      → OK
/*+ NO_INDEX(t6  ind22 ) */     → OK

• Oracle

(19c)

-- 1. テストデータ作成

drop table tab1 purge;
create table tab1(
    col1 int 
   ,col2 int
  );

drop table tab2 purge;
create table tab2(
    col1 int 
   ,col2 int
   );

drop table tab3 purge;
create table tab3(
    col1 int 
   ,col2 int
   );

declare
begin
for i in 1..1000000 loop
  insert into tab1 values(
    i
   ,floor(dbms_random.value(1, 100001) )
   );
  
  insert into tab2 values(
    i
   ,floor(dbms_random.value(1, 100001) )
   );
  insert into tab3 values(
    i
   ,floor(dbms_random.value(1, 100001) )
   );
end loop;
end;
/

commit;

select count(*) from tab1;
select * from tab1 order by dbms_random.value()  fetch first 20 rows only;
alter table tab1 add constraint tab1pk primary key (col1);
create index ind12 on tab1(col2);

select count(*) from tab2;
select * from tab2 order by dbms_random.value()  fetch first 20 rows only;
alter table tab2 add constraint tab2pk primary key (col1);
create index ind22 on tab2(col2);

select count(*) from tab3;
select * from tab3 order by dbms_random.value()  fetch first 20 rows only;
alter table tab3 add constraint tab3pk primary key (col1);
create index ind32 on tab3(col2);

set time on
set timing on

exec dbms_stats.gather_table_stats(user,'TAB1');
exec dbms_stats.gather_table_stats(user,'TAB2');
exec dbms_stats.gather_table_stats(user,'TAB3');

--2. 動作確認

explain plan for
select /* INDEX(t5   tab1pk) */  count(*) from tab1 t1
where exists ( select 1 from
  (
   select /* QB_NAME(qb1) */ /* INDEX(t21  ind22)  */   t21.col2 from tab2 t21 inner join tab3 t22
   on t21.col1 = t22.col1
   where t21.col2 < 5000
   group by t21.col2
   having count(t22.col2) > 100
  ) t2 where t1.col2 = t2.col2 )
and exists ( select 1 from
  (
   select /* QB_NAME(qb2) */ /* INDEX(t32  tab3pk) */    t31.col2 from tab2 t31 inner join tab3 t32
   on t31.col1 = t32.col1
  ) t3 where t1.col2 = t3.col2 )
and exists ( select /* QB_NAME(qb3) */ /* INDEX(t4   tab1pk) */   1 from tab1 t4 where t1.col1 = t4.col2)
and exists ( select /* QB_NAME(qb4) */ /*+ INDEX(t5   tab1pk) */   1 from tab1 t5 inner join tab2 t6 on t5.col1 = t6.col1 where t1.col1 = t5.col1 and t1.col2 = t6.col2)
;

select * from table(dbms_xplan.display(format=>'ALL') );

--1.1 問合せブロック付きヒント(システム生成) 

/*+ INDEX(t21@SEL$4  ind22)  */     → Unresolved
/*+ INDEX(t32@SEL$7  tab3pk) */     → Unresolved
/*+ INDEX(t4@SEL$9   tab1pk) */     → OK
/*+ INDEX(t5@SEL$1   tab1pk) */     → Unresolved

シンプルなサブクエリはアクセスヒント句指定可能

--1.2 問合せブロック付きヒント(ユーザ指定)

/*+ INDEX(T21@QB1   ind22)  */     → Unresolved
/*+ INDEX(T32@QB2   tab3pk) */     → Unresolved
/*+ INDEX(T4@QB3    tab1pk) */     → OK
/*+ INDEX(T5@QB4    tab1pk) */     → Unresolved

--1.3 グローバル・ヒント
/*+ INDEX(T2.T21 ind22 ) */             →グローバルヒントが認識されない 
/*+ INDEX(T3.T32 tab3pk) */             →グローバルヒントが認識されない 

--1.4 サブクエリ内部名を本体に指定

/*+ INDEX(t21  ind22)  */     → Unresolved
/*+ INDEX(t32  tab3pk) */     → Unresolved
/*+ INDEX(t4   tab1pk) */     → Unresolved
/*+ INDEX(t5   tab1pk) */     → Unresolved

--1.5 サブクエリ内部名をサブクエリに指定

/*+ INDEX(t21  ind22)  */     → OK
/*+ INDEX(t32  tab3pk) */     → OK
/*+ INDEX(t4   tab1pk) */     → OK
/*+ INDEX(t5   tab1pk) */     → OK

• PostgreSQL

(14)

-- 1. テストデータ作成

drop table tab1;
create table tab1(
    col1 bigint 
   ,col2 bigint
  );
drop table tab2;
create table tab2(
    col1 bigint 
   ,col2 bigint
   );
   
drop table tab3;
create table tab3(
    col1 bigint 
   ,col2 bigint
   );

start transaction;
insert into tab1 select
   g
  ,floor(random() * 100000)+1
from generate_series(1,1000000) g;

commit;

start transaction;
insert into tab2 select
   g
  ,floor(random() * 100000)+1
from generate_series(1,1000000) g;

commit;

start transaction;
insert into tab3 select
   g
  ,floor(random() * 100000)+1
from generate_series(1,1000000) g;

commit;

select count(*) from tab1;
select * from tab1 order by random() limit 20;
alter table tab1 add constraint tab1pk primary key (col1);
create index ind12 on tab1(col2);
select count(*) from tab2;
select * from tab2 order by random() limit 20;
alter table tab2 add constraint tab2pk primary key (col1);
create index ind22 on tab2(col2);
select count(*) from tab3;
select * from tab3 order by random() limit 20;
alter table tab3 add constraint tab3pk primary key (col1);
create index ind32 on tab3(col2);

\timing 1
\pset pager 0
set pg_hint_plan.debug_print = on;

analyze tab1;
analyze tab2;
analyze tab3;

--2. 動作確認

set pg_hint_plan.debug_print=1;
show pg_hint_plan.debug_print;

/*+ SeqScan(t5) */ 
explain
select    count(*) from tab1 t1
where exists ( select 1 from
  (
   select   t21.col2 from tab2 t21 inner join tab3 t22
   on t21.col1 = t22.col1
   where t21.col2 < 5000
   group by t21.col2
   having count(t22.col2) > 100
  ) t2 where t1.col2 = t2.col2 )
and exists ( select 1 from
  (
   select  t31.col2 from tab2 t31 inner join tab3 t32
   on t31.col1 = t32.col1
  ) t3 where t1.col2 = t3.col2 )
and exists ( select 1 from tab1 t4 where t1.col1 = t4.col2)
and exists ( select  1 from tab1 t5 inner join tab2 t6 on t5.col1 = t6.col1 where t1.col1 = t5.col1 and t1.col2 = t6.col2)
;

-- サブクエリ内部名を本体に指定

/*+ BitmapScan(t21) */        →  used hint
/*+ SeqScan(t31) */           →  used hint
/*+ SeqScan(t4) */            →  used hint
/*+ SeqScan(t5) */            →  used hint

• SQL Server

(2019)

調査観点なし