WebJun 5, 2024 · Hive converts joins over multiple tables into a single map/reduce job if for every table the same column is used in the join clauses e.g. SELECT a.val, b.val, c.val FROM a JOIN b ON (a.key = b.key1) JOIN c ON (c.key = b.key1) is converted into a single map/reduce job as only key1 column for b is involved in the join. On the other hand. http://duoduokou.com/sql/65083727821265450237.html
hive多表查询的条件写在join里好还是用子查询? - 知乎
WebSql 在配置单元中按日期重复以前的值,sql,hive,Sql,Hive. ... with join_table as ( select coleasce(t1.date, t2.date) as date, t2.id, t2.amount from table1 as t1 outer join table2 as t2 on t1.date = t2.date ) , rank_table as ( select *, SUM(id) OVER (ORDER BY d_day ROWS BETWEEN unbounded preceding and CURRENT ROW) as id_rnk, SUM ... WebOct 11, 2024 · 2、查看filter_log表strpicdownloadimgmd5个数,6亿左右,做distinct之后,只有5亿。. 大约有1亿重复数据。. 3、如果一个key在user表和filter_log表中都重复出现1k次,两个表join,总数据量为1k*1k=100w,也就说这一个key的结果就有100w条。. 这还只是1k次,如果是10w呢?. peterborough marathon
left join 和left semi join - 简书
Webhive 中join类型. hive中支持传统数据库中的inner join、left outer join、right outer join、full join,还支持left semi join和cross join 其中 inner join、left outer join、right outer join、full join 和传统数据join类型用法一样。 left semi join 以left semi join关键字… 2024/4/14 23:07:18 Webleft join在我们使用mysql查询的过程中可谓非常常见,比如博客里一篇文章有多少条评论、商城里一个货物有多少评论、一条评论有多少个赞等等。. 但是由于对join、on、where等关键字的不熟悉,有时候会导致查询结果与预期不符,所以今天我就来总结一下,一起避 ... WebFeb 24, 2024 · 由于 hive 中没有 in/exist 这样的子句(新版将支持),所以需要将这种类型的子句转成 left semi join。. left semi join 是只传递表的 join key 给 map 阶段 , 如果 key 足够小还是执行 map join, 如果不是则还是 common join。. 关于 common join(shuffle join/reduce join)的原理请参考文末 ... star flare search and rescue