如果在连接的表中有一张是小表,在map阶段完全可以将小表读到内存中,直接在map端进行join,这种操作可以明显降低join所耗费的时间 select /*+MAPJOIN(t1)*/ t1.id,t2.id from table1 t1 join table2 t2 on t1.id=t2.id --如果想让hive自动开启这个优化,设置hive.auto.convert.join=true(这样hive会在必...
row_number() over (partiotion by A1,B2 by C2) as r2, row_number() over (partiotion by A1,C2 by B2) as r3 from A,B,C where A.A1 = B.B1 and A.A1 = C.C1 ) T
一个SQL语句应该很难写出来。一般可以建立两个函数，分别为取courseid，和coursename。然后，根据表1，调用函数就可以了。create function get_courseid ( @uid int )returns varchar(100)as begin declare @c varchar(100)set @c = ''select @c = @c + cast ( courseid as varchar(10)) +...
不采用left join或full join也可以 3 回答慕的地6264312 TA贡献1817条经验 获得超6个赞 A表 A1 B表 B1,B2 C表C1,C2 SQL如下 1 2 3 4 5 6 7 8 9 10 11 select case r1 when 1 then A1 else '' end as A1, case r2 when 1 then B2 else '' end as B2, case r3 when 1 then C2 el...
不采用left join或full join也可以子衿沉夜 浏览2418回答3 3回答 慕的地6264312 A表 A1B表 B1,B2C表C1,C2SQL如下1234567891011select case r1 when 1 then A1 else '' end as A1, case r2...