调用sqlContext.udf.register()
此时注册的方法 只能在sql()中可见,对DataFrame API不可见
用法:sqlContext.udf.register("makeDt", makeDT(_:String,_:String,_:String))
示例:
def makeDT(date: String, time: String, tz: String) = s"$date $time $tz"
sqlContext.udf.register("makeDt", makeDT(_:String,_:String,_:String))
// Now we can use our function directly in SparkSQL.
sqlContext.sql("SELECT amount, makeDt(date, time, tz) from df").take(2)
// but not outside
df.select($"customer_id", makeDt($"date", $"time", $"tz"), $"amount").take(2) // fails
2)调用spark.sql.function.udf()方法
此时注册的方法,对外部可见
用法:valmakeDt = udf(makeDT(_:String,_:String,_:String))
示例:
import org.apache.spark.sql.functions.udf
val makeDt = udf(makeDT(_:String,_:String,_:String))
// now this works
df.select($"customer_id", makeDt($"date", $"time", $"tz"), $"amount").take(2)