在连接表之间使用 OR 条件进行查询的性能

Question

有两个表，tparent 和 tchild，它们是使用脚本 #1 创建的。 需要查询uname等于'sky'的两个表中的所有信息。 当只有少量记录时，以下查询语句 #2 很快。 但是当使用以下脚本#3 插入大量记录时，它会变得非常缓慢。 我认为这是由表之间的 OR 条件引起的，索引对查询没有用处。 所以我得到了一个快速的解决方案，将语句更改为三个子语句和联合结果，如#4。 我想知道有没有更好的解决方案？那是什么？

谢谢！

#1

drop table tparent;
drop table tchild;
create table tparent(typeid int,sno number,uname varchar2(50) );
create table tchild(typeid int,sno number,seqno int,uname varchar2(50));
create unique index uidx_tparent_typeidsno on tparent(typeid,sno);
create unique index uidx_tchild_typeidsnoseqno on tchild(typeid,sno,seqno);
create index idx_tparent_name on tparent(uname);
create index idx_tchild_name on tchild(uname);

insert into tparent values (1,10,'lily');
insert into tparent values (1,11,'eric');
insert into tparent values (2,10,'tom');
insert into tparent values (2,11,'eric');
insert into tparent values (3,10,'sky');

insert into tchild values (1,10,1,'sam');
insert into tchild values (1,10,2,'sky');
insert into tchild values (1,11,1,'eric');
insert into tchild values (1,11,2,'john');
insert into tchild values (2,10,1,'sky');
insert into tchild values (2,11,1,'eric');
insert into tchild values (3,10,1,'tony');

#2

select p.typeid,p.sno,p.uname,c1.uname as uname1,c2.uname as uname2 from tparent p
  left join tchild c1 on c1.typeid=p.typeid and c1.sno = p.sno and c1.seqno=1
  left join tchild c2 on c2.typeid=p.typeid and c2.sno = p.sno and c2.seqno=2
where (p.uname='sky' or c1.uname='sky' or c2.uname='sky');

#3

BEGIN
    FOR x IN 1..10
    LOOP
        BEGIN
            FOR y IN 10000..100000
            LOOP
                BEGIN
                    insert into tparent values (x,y,'name'|| y);
                    insert into tchild values (x,y,1,'name'|| y);
                    insert into tchild values (x,y,2,'name'|| y);
                END;
            END LOOP;
            COMMIT;
        END;
    END LOOP;
END;

#4

select typeid,sno,max(uname),max(uname1),max(uname2) from (

select p.typeid,p.sno,p.uname,c1.uname as uname1,c2.uname as uname2 from tparent p
  left join tchild c1 on c1.typeid=p.typeid and c1.sno = p.sno and c1.seqno=1
  left join tchild c2 on c2.typeid=p.typeid and c2.sno = p.sno and c2.seqno=2
where (p.uname='sky' )
union 
select p.typeid,p.sno,p.uname,c1.uname as uname1,c2.uname as uname2 from tparent p
  left join tchild c1 on c1.typeid=p.typeid and c1.sno = p.sno and c1.seqno=1
  left join tchild c2 on c2.typeid=p.typeid and c2.sno = p.sno and c2.seqno=2
where ( c1.uname='sky' )
union

select p.typeid,p.sno,p.uname,c1.uname as uname1,c2.uname as uname2 from tparent p
  left join tchild c1 on c1.typeid=p.typeid and c1.sno = p.sno and c1.seqno=1
  left join tchild c2 on c2.typeid=p.typeid and c2.sno = p.sno and c2.seqno=2
where ( c2.uname='sky')
) tb group by typeid,sno
order by typeid,sno
;

Answer 1

您应该在 from 子句中使用“union all”，然后按 group by。