如何在Pyspark中连接两列，但影响单个行的连接顺序？

from pyspark.sql import SparkSession
from pyspark.sql.functions import concat, when

spark = SparkSession.builder.getOrCreate()

data = [("John", "Doe"), ("Jane", "Smith"), ("Bob", "Johnson")]
df = spark.createDataFrame(data, ["first_name", "last_name"])

df = df.withColumn("full_name", when(df.first_name < df.last_name, concat(df.first_name, df.last_name))
                                 .otherwise(concat(df.last_name, df.first_name)))

df.show()