サブクエリとleading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  /*+ JOIN_PREFIX(t1 , t6,t5) */   count(*) from tab1 t1
where exists ( select 1 from
  (
   select /* QB_NAME(qb1) */ /* JOIN_PREFIX(t22 , t21) */   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) */ /* JOIN_PREFIX(t32 , t31) */   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) */ 1 from tab1 t4 where t1.col1 = t4.col2)
and exists ( select /* QB_NAME(qb4) */ /* JOIN_PREFIX(t6  , t5) */   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
/*+ JOIN_PREFIX(t32@qb2 , t1  ) */     → OK
/*+ JOIN_PREFIX(t22@qb1 , t1  ) */     → Unresolved
/*+ JOIN_PREFIX(t4@qb3  , t1 ) */      → OK
/*+ JOIN_PREFIX(t5@qb4  , t1 ) */      → OK

グループ化したサブクエリ内のテーブルはleadingヒント句に指定不可能

-- サブクエリ名を指定

/*+ JOIN_PREFIX(t3 ,t1) */     → Unresolved
/*+ JOIN_PREFIX(t1 ,t2) */     → OK

グループ化していないサブクエリはleadingヒント句に指定不可能
グループ化したサブクエリはleadingヒント句に指定可能

-- サブクエリ内部名を本体に指定

/*+ JOIN_PREFIX(t1 , t32) */    → OK
/*+ JOIN_PREFIX(t1 , t22) */    → Unresolved
/*+ JOIN_PREFIX(t1 , t4) */     → OK
/*+ JOIN_PREFIX(t1 , t6) */     → OK

-- サブクエリ内部名をサブクエリに指定

/*+ JOIN_PREFIX(t32 , t31) */    → 警告はでないが実行計画変化なし
/*+ JOIN_PREFIX(t22 , t21) */    → OK
/*+ JOIN_PREFIX(t6  , t5) */     → 警告はでないが実行計画変化なし

• 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 /* LEADING(T1 T6) */   count(*) from tab1 t1
where exists ( select 1 from
  (
   select /* QB_NAME(qb1) */ /* LEADING(T22 T21) */   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) */ /* LEADING(T31 T32) */  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) */ 1 from tab1 t4 where t1.col1 = t4.col2)
and exists ( select /* QB_NAME(qb4) */ /*+ LEADING(T5 T6) */   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) 
/*+ LEADING(T32@SEL$7 T1@SEL$2 ) */     → Unused
/*+ LEADING(T22@SEL$4 T1@SEL$2 ) */     → Unused
/*+ LEADING(T4@SEL$9  T1@SEL$2 ) */     → OK
/*+ LEADING(T5@SEL$1  T1@SEL$2 ) */     → Unused

シンプルなサブクエリはleading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)
/*+ LEADING(T32@qb2 T1  ) */     → Unused
/*+ LEADING(T22@qb1 T1  ) */     → Unused
/*+ LEADING(T4@qb3  T1 ) */      → OK
/*+ LEADING(T5@qb4  T1 ) */      → Unused

--1.3 グローバル・ヒント
/*+ LEADING(T3.T32 T1 ) */         →グローバルヒントが認識されない 
/*+ LEADING(T3.T32) */             →グローバルヒントが認識されない 

--1.4 サブクエリ名を指定

/*+ LEADING(T1 T3) */    → Unused
/*+ LEADING(T1 T2) */     → OK

グループ化していないサブクエリはleadingヒント句に指定不可能
グループ化したサブクエリはleadingヒント句に指定可能

--1.5 サブクエリ内部名を本体に指定

/*+ LEADING(T1 T32) */    → Unused
/*+ LEADING(T1 T22) */    → Unused
/*+ LEADING(T1 T4) */     → OK
/*+ LEADING(T1 T6) */     → Unused

--1.6 サブクエリ内部名をサブクエリに指定

/*+ LEADING(T31 T32) */    → OK
/*+ LEADING(T22 T21) */    → OK
/*+ LEADING(T5 T6) */      → OK

--1.7 leadingヒントを本体とインラインビューに両方指定した場合の挙動

/*+ LEADING(T2) */ と /*+ LEADING(T22 T21) */  の組み合わせは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;

/*+ Leading(t1 t32) */ 
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)
;

-- サブクエリ名を指定

/*+ Leading(t1 t3) */     → not used hint
/*+ Leading(t1 t2) */     → used hint

グループ化していないサブクエリはleadingヒント句に指定不可能
グループ化したサブクエリはleadingヒント句に指定可能

-- サブクエリ内部名を本体に指定

/*+ Leading(t1 t32) */     → used hint
/*+ Leading(t1 t22) */     → not used hint
/*+ Leading(t1 t4) */      → used hint
/*+ Leading(t1 t6) */      → used hint

• SQL Server

(2019)

-- 1. テストデータ作成

drop table tab1;
create table tab1(
    col1 bigint not null
   ,col2 bigint
   );

drop table tab2;
create table tab2(
    col1 bigint not null
   ,col2 bigint
   );

drop table tab3;
create table tab3(
    col1 bigint not null
   ,col2 bigint
   );

set nocount on
declare @i int;
set @i = 1;
begin transaction;
while @i <= 1000000
begin
  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
    );
 set @i = @i + 1;
end
commit;

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

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

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

set statistics time on

update statistics tab1;
update statistics tab2;
update statistics tab3;

--2. 動作確認

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)
OPTION (FORCE ORDER)
;

FORCE ORDERクエリヒントしかないので、SQL文組み換えと合わせて適用する

※サブクエリについてもFORCE ORDERは有効