从sql server导入数据到spark local

我想使用JDBC驱动程序从sql server导入一个表到spark local，并在其上运行spark sql。我下载了sqljdbc for sql server，并将这一行添加到conf目录下的spark-env.sh中:

SPARK_CLASSPATH= "C:/Program Files/Microsoft SQL Server/sqljdbc_4.0/enu/sqljdbc4.jar" ./bin/spark-shell

如此处所示

df = sqlContext.load(source="jdbc", url="jdbc:sqlserver:dd", dbtable="Reporting.dbo.datatable")

但是，它抛出一个错误:

Py4JJavaError: An error occurred while calling o28.load.
: java.sql.SQLException: No suitable driver found for jdbc:sqlserver:PC-BFS2
        at java.sql.DriverManager.getConnection(Unknown Source)
        at java.sql.DriverManager.getConnection(Unknown Source)
        at org.apache.spark.sql.jdbc.JDBCRDD$.resolveTable(JDBCRDD.scala:118)
        at org.apache.spark.sql.jdbc.JDBCRelation.<init>(JDBCRelation.scala:128)
        at org.apache.spark.sql.jdbc.DefaultSource.createRelation(JDBCRelation.scala:113)
        at org.apache.spark.sql.sources.ResolvedDataSource$.apply(ddl.scala:269)
        at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:114)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
        at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:379)
        at py4j.Gateway.invoke(Gateway.java:259)
        at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
        at py4j.commands.CallCommand.execute(CallCommand.java:79)
        at py4j.GatewayConnection.run(GatewayConnection.java:207)
        at java.lang.Thread.run(Unknown Source)