This will help adding a column from a table to another when we "just" want to glue it without the same column. Here, we would need to use the "row_index" which will behave like a same column.

add_column_from_anotherDF.java

import static org.apache.spark.sql.functions.*;

result = result.withColumn("row_index", row_number().over(Window.orderBy(monotonically_increasing_id())));
DF = DF.withColumn("row_index", row_number().over(Window.orderBy(monotonically_increasing_id())));

result = result.join(DF.withColumn("realBMI",col("BMI")).select("row_index", "realBMI"), result.col("row_index").equalTo(DF.col("row_index")));
result = result.drop("row_index");
result.show();

From this stacktrace: https://stackoverflow.com/questions/42853778/add-a-column-from-another-dataframe