需下载 MySQL JDBC Connector 库，并将其复制到$SQOOP_HOME/lib
下载mysql jdbc连接库
地址：
[zhouhh@Hadoop48 ~]$ wget ://cdn.mysql.com/
[zhouhh@Hadoop48 mysql-connector-Java-5.1.21]$ cp mysql-connector-java-5.1.21-bin.jar ../sqoop/lib/.
[zhouhh@Hadoop48 ~]$ sqoop list-tables --connect jdbc:mysql://localhost/toplists --username root
t1
[zhouhh@Hadoop48 ~]$ sqoop-export --connect jdbc:mysql://localhost/toplists --username root --table t1 --export-dir /hbase
java.io.IOException: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at org.apache.sqoop.mapreduce.ExportOutputFormat.getRecordWriter(ExportOutputFormat.java:79)
at org.apache.hadoop.mapred.MapTask$NewDirectOutputCollector.<init>(MapTask.java:628)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:753)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
这是可能由jdbc版本引起的，换成5.1.18
[zhouhh@Hadoop48 ~]$ sqoop-export --connect jdbc:mysql://localhost:3306/toplists --username root --table t1 --export-dir /hbase
Error initializing attempt_201206271529_0006_r_000000_0:
org.apache.hadoop.util.DiskChecker$DiskErrorException: Could not find any valid local directory for ttprivate/taskTracker/zhouhh/jobcache/job_201206271529_0006/jobToken
at org.apache.hadoop.fs.LocalDirAllocator$AllocatorPerContext.getLocalPathForWrite(LocalDirAllocator.java:381)
at org.apache.hadoop.fs.LocalDirAllocator.getLocalPathForWrite(LocalDirAllocator.java:146)
at org.apache.hadoop.fs.LocalDirAllocator.getLocalPathForWrite(LocalDirAllocator.java:127)
at org.apache.hadoop.mapred.TaskTracker.localizeJobTokenFile(TaskTracker.java:4271)
at org.apache.hadoop.mapred.TaskTracker.initializeJob(TaskTracker.java:1177)
at org.apache.hadoop.mapred.TaskTracker.localizeJob(TaskTracker.java:1118)
at org.apache.hadoop.mapred.TaskTracker$5.run(TaskTracker.java:2430)
at java.lang.Thread.run(Thread.java:722)
DiskErrorException ，定位半天，发现是另一台机器的空间满了，在mapreduce运行时会引起该异常。
[zhouhh@Hadoop46 ~]$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 28337624 26877184 0 100% /
[zhouhh@Hadoop48 ~]$ sqoop-export --connect jdbc:mysql://192.168.10.48:3306/toplists --username root --table t1 --export-dir /hbase
Caused by: java.sql.SQLException: null, message from server: "Host 'Hadoop47' is not allowed to connect to this MySQL server"
这是权限问题，设置授权：
mysql> GRANT ALL PRIVILEGES ON *.* TO '%'@'%';#允许所有用户查看和修改databaseName数据库模式的内容，否则别的IP连不上本MYSQL
Query OK, 0 rows affected (0.06 sec)
这是测试，所以权限没有限制。实际工作环境需谨慎授权。
[zhouhh@Hadoop48 ~]$ sqoop-export --connect jdbc:mysql://192.168.10.48:3306/toplists --username root --table t1 --export-dir /hbase
Note: /tmp/sqoop-zhouhh/compile/fa1d1c042030b0ec8537c7a4cd02aab3/t1.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
java.lang.NumberFormatException: For input string: "7"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:481)
at java.lang.Integer.valueOf(Integer.java:582)
at t1.__loadFromFields(t1.java:218)
at t1.parse(t1.java:170)
at org.apache.sqoop.mapreduce.TextExportMapper.map(TextExportMapper.java:77)
at org.apache.sqoop.mapreduce.TextExportMapper.map(TextExportMapper.java:36)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
at org.apache.sqoop.mapreduce.AutoProgressMapper.run(AutoProgressMapper.java:183)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
at org.apache.hadoop.mapred.Child.main(Child.java:249)
这是由于/hbase是hbase的库表，根本不是可以导的格式，所以报错。
[zhouhh@Hadoop48 ~]$ sqoop-export --connect jdbc:mysql://192.168.10.48:3306/toplists --username root --table t1 --export-dir /hbase/t1
[zhouhh@Hadoop48 ~]$ sqoop-export --verbose --connect jdbc:mysql://192.168.10.48:3306/toplists --username root --table t1 --update-key id --input-fields-terminated-by '\t' --export-dir /hbase/t1
Note: /tmp/sqoop-zhouhh/compile/8ce6556eb13b3000550a9c864eaa6820/t1.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
[zhouhh@Hadoop48 ~]$
但将导出目录指到/hbase/t1表中，导出不会报错，而mysql中没有数据。后面才了解到，sqoop没有直接从hbase中将表导出到mysql的办法。必须先将hbase导出成平面文件，或者导出到hive中，才可以用sqoop将数据导出到mysql。