Left outer join results in all rows from statesPopulationDF, including any common in statesPopulationDF and statesTaxRatesDF.

Join the two datasets by the state column, shown as follows:

val joinDF = statesPopulationDF.join(statesTaxRatesDF, statesPopulationDF("State") === statesTaxRatesDF("State"), "leftouter")

%sql
val joinDF = spark.sql("SELECT * FROM statesPopulationDF LEFT OUTER JOIN statesTaxRatesDF ON statesPopulationDF.State = statesTaxRatesDF.State")

scala> joinDF.count
res22: Long = 357

scala> joinDF.show(5)
+----------+----+----------+----------+-------+
| State|Year|Population| State|TaxRate|
+----------+----+----------+----------+-------+
| Alabama|2010| 4785492| Alabama| 4.0|
| Alaska|2010| 714031| null| null|
| Arizona|2010| 6408312| Arizona| 5.6|
| Arkansas|2010| 2921995| Arkansas| 6.5|
|California|2010| 37332685|California| 7.5|
+----------+----+----------+----------+-------+