Spark SQL:如何将新行追加到dataframe表(来自另一个表)

Question

我正在使用带有数据帧的Spark SQL.我有一个输入数据帧,我想将其行追加(或插入)到具有更多列的更大的数据帧.我该怎么办？

如果这是SQL,我会使用INSERT INTO OUTPUT SELECT ... FROM INPUT,但我不知道如何使用Spark SQL.

具体:

var input = sqlContext.createDataFrame(Seq(
        (10L, "Joe Doe", 34),
        (11L, "Jane Doe", 31),
        (12L, "Alice Jones", 25)
        )).toDF("id", "name", "age")

var output = sqlContext.createDataFrame(Seq(
        (0L, "Jack Smith", 41, "yes", 1459204800L),
        (1L, "Jane Jones", 22, "no", 1459294200L),
        (2L, "Alice Smith", 31, "", 1459595700L)
        )).toDF("id", "name", "age", "init", "ts")


scala> input.show()
+---+-----------+---+
| id|       name|age|
+---+-----------+---+
| 10|    Joe Doe| 34|
| 11|   Jane Doe| 31|
| 12|Alice Jones| 25|
+---+-----------+---+

scala> input.printSchema()
root
 |-- id: long (nullable = false)
 |-- name: string (nullable = true)
 |-- age: integer (nullable = false)


scala> output.show()
+---+-----------+---+----+----------+
| id|       name|age|init|        ts|
+---+-----------+---+----+----------+
|  0| Jack Smith| 41| yes|1459204800|
|  1| Jane Jones| 22|  no|1459294200|
|  2|Alice Smith| 31|    |1459595700|
+---+-----------+---+----+----------+

scala> output.printSchema()
root
 |-- id: long (nullable = false)
 |-- name: string (nullable = true)
 |-- age: integer (nullable = false)
 |-- init: string (nullable = true)
 |-- ts: long (nullable = false)

我想将所有行追加input到末尾output.同时,我想将output列设置为init空字符串'',并将ts列设置为当前时间戳,例如1461883875L.

任何帮助,将不胜感激.

Answer 1

Spark DataFrames是不可变的,因此无法追加/插入行.相反,您只需添加缺少的列并使用UNION ALL:

output.unionAll(input.select($"*", lit(""), current_timestamp.cast("long")))