PySpark:将nullType字段转换为结构类型列下的字符串

from pyspark.sql import SparkSession
from pyspark.sql.functions import col, when
from pyspark.sql.types import StringType

spark = SparkSession.builder.appName("NullType to String").getOrCreate()

data = [(1, "John", None), (2, "Alice", "25"), (3, "Bob", None)]
df = spark.createDataFrame(data, ["id", "name", "age"])

df = df.withColumn("age", when(col("age").isNull(), "Unknown").otherwise(col("age").cast(StringType())))

df.show()

+---+----+-------+
| id|name|    age|
+---+----+-------+
|  1|John|Unknown|
|  2|Alice|     25|
|  3| Bob|Unknown|
+---+----+-------+