scala - Joining two dataframes without a common column

Question

I have two dataframes which has different types of columns. I need to join those two different dataframe. Please refer the below example

val df1 has
Customer_name 
Customer_phone
Customer_age

val df2 has
Order_name
Order_ID

These two dataframe doesn't have any common column. Number of rows and Number of columns in the two dataframes also differs. I tried to insert a new dummy column to increase the row_index value as below val dfr=df1.withColumn("row_index",monotonically_increasing_id()).

But as i am using Spark 2, monotonically_increasing_id method is not supported. Is there any way to join two dataframe, so that I can create the value of two dataframe in a single sheet of excel file.

For example

val df1:
Customer_name  Customer_phone  Customer_age
karti           9685684551     24      
raja            8595456552     22

val df2:
Order_name Order_ID
watch       1
cattoy     2

My final excel sheet should be like this:

Customer_name  Customer_phone  Customer_age   Order_name  Order_ID

karti          9685684551      24             watch        1
   
raja           8595456552      22             cattoy      2

Answer 1

add an index column to both dataframe using the below code

df1.withColumn("id1",monotonicallyIncreasingId)
df2.withColumn("id2",monotonicallyIncreasingId)

then join both the dataframes using the below code and drop the index column

df1.join(df2,col("id1")===col("id2"),"inner")
   .drop("id1","id2")