Scala: Using a spark sql function when selecting column from a dataframe

Question

I have a two table/dataframe: A and B

A has following columns: cust_id, purch_date

B has one column: cust_id, col1 (col1 is not needed)

Following sample shows content of each table:

Table A
cust_id  purch_date
  34564  2017-08-21
  34564  2017-08-02
  34564  2017-07-21
  23847  2017-09-13
  23423  2017-06-19


Table B
cust_id  col1
  23442     x
  12452     x
  12464     x  
  23847     x
  24354     x

I want to select the cust_id and first day of month of purch_date where the selected cust_id are not there in B.

This can be achieved in SQL by following command:

select a.cust_id, trunc(purch_date, 'MM') as mon
from a
left join b
on a.cust_id = b.cust_id
where b.cust_id is null
group by cust_id, mon;

Following will be the output:

Table A
cust_id  purch_date
  34564  2017-08-01
  34564  2017-07-01
  23423  2017-06-01

I tried the following to implement the same in Scala:

import org.apache.spark.sql.functions._

a = spark.sql("select * from db.a")
b = spark.sql("select * from db.b")

var out = a.join(b, Seq("cust_id"), "left")
           .filter("col1 is null")
           .select("cust_id", trunc("purch_date", "month"))
           .distinct()

But I am getting different errors like:

error: type mismatch; found: StringContext required: ?{def $: ?}

I am stuck here and couldn't find enough documentation/answers on net.

1pluszara · Accepted Answer · 2019-02-23T07:13:46.190

Select should contain Columns instead of Strings:

Input:

df1:
+-------+----------+
|cust_id|purch_date|
+-------+----------+
|  34564|2017-08-21|
|  34564|2017-08-02|
|  34564|2017-07-21|
|  23847|2017-09-13|
|  23423|2017-06-19|
+-------+----------+    

df2:
+-------+----+
|cust_id|col1|
+-------+----+
|  23442|   X|
|  12452|   X|
|  12464|   X|
|  23847|   X|
|  24354|   X|
+-------+----+

Change your query as below:

df1.join(df2, Seq("cust_id"), "left").filter("col1 is null")
.select($"cust_id", trunc($"purch_date", "MM"))
.distinct()
.show()

Output:

+-------+---------------------+
|cust_id|trunc(purch_date, MM)|
+-------+---------------------+
|  23423|           2017-06-01|
|  34564|           2017-07-01|
|  34564|           2017-08-01|
+-------+---------------------+

Scala: Using a spark sql function when selecting column from a dataframe

1 Answers1