spark sql中保存数据的几种方式

从官网来copy过来的几种模式描述：

Scala/Java	Python	Meaning
SaveMode.ErrorIfExists(default)	"error"(default)	When saving a DataFrame to a data source, if data already exists, an exception is expected to be thrown.
SaveMode.Append	"append"	When saving a DataFrame to a data source, if data/table already exists, contents of the DataFrame are expected to be appended to existing data.
SaveMode.Overwrite	"overwrite"	Overwrite mode means that when saving a DataFrame to a data source, if data/table already exists, existing data is expected to be overwritten by the contents of the DataFrame.
SaveMode.Ignore	"ignore"	Ignore mode means that when saving a DataFrame to a data source, if data already exists, the save operation is expected to not save the contents of the DataFrame and to not change the existing data. This is similar to a `CREATE TABLE IF NOT EXISTS` in SQL.

ErrorIfExists就是出现错误后，抛出错误 

Append顾名思义，就是追加信息

Overwrite是覆盖

Ignore是如果存在则忽略

另外，如果没有指定存储模式，那么默认应该是SaveMode.ErrorIfExists，因为我重复保存后报了：already exists错误来着。

如何使用：

import org.apache.spark.sql._
val sqlContext = new org.apache.spark.sql.SQLContext(sc)
val df = sqlContext.load("/opt/modules/spark1.3.1/examples/src/main/resources/people.json")
 df.save("/opt/test/1","json", SaveMode.Overwrite)  //可以把SaveMode.Overwrite换成其他的几种形式喽