SQL查询/ Spark数据帧到外部联接并减去两个表的值

Question

I'm looking to do an outer join on two tables A and B based on 'name', and then subtract the column 'count' values, substituting 0 if the row doesn't exist in the other table. Does anyone know a simple SQL query to make this possible?

A
name count
ABC 10
DEF 10
GHI 20

B
name count
ABC 20
GHI 30
XYZ 10

RESULT
name count
ABC -10
DEF 10
GHI -10
XYZ -10

Thanks!

(or if there is a way to do this with Spark DataFrames that would be great as well!)

Answer 1

With spark , you can join the two data frames on name column, coalesce null count to zero and then subtract A.count with B.count :

(A.alias("a").join(B.alias("b"), Seq("name"), "outer")
  .selectExpr("name", "coalesce(a.count, 0) - coalesce(b.count, 0) as count")).show
+----+-----+
|name|count|
+----+-----+
| DEF|   10|
| GHI|  -10|
| XYZ|  -10|
| ABC|  -10|
+----+-----+