如果表不存在，这里是我创建表的方法。

session.execute(
                  "CREATE TABLE simplex.songs (" +
                        "id uuid PRIMARY KEY," + 
                        "title text," + 
                        "album text," + 
                        "artist text," + 
                        "tags set<text>," + 
                        "data blob" + 
                        ") IF NOT EXISTS ;");
            session.execute(
                  "CREATE TABLE simplex.playlists (" +
                        "id uuid," +
                        "title text," +
                        "album text, " + 
                        "artist text," +
                        "song_id uuid," +
                        "PRIMARY KEY (id, title, album, artist)" +
                        ") IF NOT EXISTS ;");
    }

运行此命令时，出现以下错误：

Exception in thread "main" com.datastax.driver.core.exceptions.SyntaxError: line 1:108 missing EOF at 'IF'
    at com.datastax.driver.core.exceptions.SyntaxError.copy(SyntaxError.java:35)
    at com.datastax.driver.core.DefaultResultSetFuture.extractCauseFromExecutionException(DefaultResultSetFuture.java:175)
    at com.datastax.driver.core.DefaultResultSetFuture.getUninterruptibly(DefaultResultSetFuture.java:147)
    at com.datastax.driver.core.SessionManager.execute(SessionManager.java:79)
    at com.datastax.driver.core.SessionManager.execute(SessionManager.java:75)
    at com.example.cassandra.simple_client.SimpleClient.createSchema(SimpleClient.java:38)
    at com.example.cassandra.simple_client.SimpleClient.main(SimpleClient.java:130)
Caused by: com.datastax.driver.core.exceptions.SyntaxError: line 1:108 missing EOF at 'IF'
    at com.datastax.driver.core.DefaultResultSetFuture.convertException(DefaultResultSetFuture.java:209)
    at com.datastax.driver.core.DefaultResultSetFuture.onSet(DefaultResultSetFuture.java:110)
    at com.datastax.driver.core.RequestHandler.setFinalResult(RequestHandler.java:210)
    at com.datastax.driver.core.RequestHandler.onSet(RequestHandler.java:325)
    at com.datastax.driver.core.Connection$Dispatcher.messageReceived(Connection.java:557)
    at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
    at org.jboss.netty.handler.codec.oneone.OneToOneDecoder.handleUpstream(OneToOneDecoder.java:70)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
    at org.jboss.netty.handler.codec.oneone.OneToOneDecoder.handleUpstream(OneToOneDecoder.java:68)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
    at org.jboss.netty.handler.codec.frame.FrameDecoder.unfoldAndFireMessageReceived(FrameDecoder.java:462)
    at org.jboss.netty.handler.codec.frame.FrameDecoder.callDecode(FrameDecoder.java:443)
    at org.jboss.netty.handler.codec.frame.FrameDecoder.messageReceived(FrameDecoder.java:303)
    at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:559)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255)
    at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:88)
    at org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:108)
    at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318)
    at org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:89)
    at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178)
    at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108)
    at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:724)