在Impala SQL中组合左连接和内连接时的连接顺序控制
在Impala SQL中组合左连接和内连接时的连接顺序控制
提问于 2017-12-12 19:57:51
有了这种数据
create table table_a as select 1 as id1;
insert into table_a values (2),(3);
create table table_b as select 1 as id1, 'a' as id2;
insert into table_b values (1,'b');
create table table_c as select 'a' as id2;我在Impala sql中有以下类型的连接：
select *
from table_a as a
left join table_b as b
on b.id1 = a.id1
left join table_c as c
on c.id2 = b.id2产生这样的结果
"id1","id1","id2","id2"
1,1,b,
1,1,a,a
2,,,
3,,,我希望第二个连接是内连接而不是左连接：
select *
from table_a as a
left join table_b as b
on b.id1 = a.id1
join table_c as c /* <- How to process this join first without using inner queries? */
on c.id2 = b.id2并得到以下结果：
"id1","id1","id2","id2"
1,1,a,a
2,,,
3,,,因此，我希望先进行table_b和table_c的内部连接，然后再进行table_a和(table_b内部连接到table_b)之间的左连接。
是否有可能在不使用内部查询的情况下以这种方式确定连接顺序？
回答 1
Stack Overflow用户
发布于 2017-12-12 21:50:44
在@jarlh的帮助下，我实现了从左到右的连接处理，然后发现可以使用右连接：
select *
from table_c as c
join table_b as b
on b.id2 = c.id2
right join table_a as a
on a.id1 = b.id1;为了得到想要的结果：
"id2","id1","id2","id1"
a,1,a,1
,,,2
,,,3页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/47772073
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