sandynz opened a new issue, #20258:
URL: https://github.com/apache/shardingsphere/issues/20258
## Bug Report
### Which version of ShardingSphere did you use?
master branch, 0bcf67adffa0c617892cab0c318e0d79992145a5
### Which project did you use? ShardingSphere-JDBC or ShardingSphere-Proxy?
proxy
### Expected behavior
No exception thrown
### Actual behavior
Error occur:
```
mysql> use sys
Database changed
mysql> select count(1) from sharding_db.t_order;
ERROR 1999 (42000): Unknown exception: null
```
Error log in proxy:
```
[ShardingSphere-Command-0] o.a.s.p.f.c.CommandExecutorTask - Exception
occur:
java.lang.NullPointerException: null
at
org.apache.shardingsphere.proxy.backend.communication.jdbc.statement.JDBCBackendStatement.setFetchSize(JDBCBackendStatement.java:81)
at
org.apache.shardingsphere.proxy.backend.communication.jdbc.statement.JDBCBackendStatement.createStorageResource(JDBCBackendStatement.java:52)
at
org.apache.shardingsphere.proxy.backend.communication.jdbc.statement.JDBCBackendStatement.createStorageResource(JDBCBackendStatement.java:42)
at
org.apache.shardingsphere.infra.executor.sql.prepare.driver.jdbc.builder.StatementExecutionUnitBuilder.createStatement(StatementExecutionUnitBuilder.java:44)
at
org.apache.shardingsphere.infra.executor.sql.prepare.driver.jdbc.builder.StatementExecutionUnitBuilder.build(StatementExecutionUnitBuilder.java:39)
at
org.apache.shardingsphere.infra.executor.sql.prepare.driver.jdbc.builder.StatementExecutionUnitBuilder.build(StatementExecutionUnitBuilder.java:34)
at
org.apache.shardingsphere.infra.executor.sql.prepare.driver.DriverExecutionPrepareEngine.createExecutionGroup(DriverExecutionPrepareEngine.java:94)
at
org.apache.shardingsphere.infra.executor.sql.prepare.driver.DriverExecutionPrepareEngine.group(DriverExecutionPrepareEngine.java:85)
at
org.apache.shardingsphere.infra.executor.sql.prepare.AbstractExecutionPrepareEngine.prepare(AbstractExecutionPrepareEngine.java:62)
at
org.apache.shardingsphere.proxy.backend.communication.ProxySQLExecutor.useDriverToExecute(ProxySQLExecutor.java:187)
at
org.apache.shardingsphere.proxy.backend.communication.ProxySQLExecutor.execute(ProxySQLExecutor.java:153)
at
org.apache.shardingsphere.proxy.backend.communication.ProxySQLExecutor.execute(ProxySQLExecutor.java:147)
at
org.apache.shardingsphere.proxy.backend.communication.jdbc.JDBCDatabaseCommunicationEngine.execute(JDBCDatabaseCommunicationEngine.java:132)
at
org.apache.shardingsphere.proxy.frontend.mysql.command.query.text.query.MySQLComQueryPacketExecutor.execute(MySQLComQueryPacketExecutor.java:94)
at
org.apache.shardingsphere.proxy.frontend.command.CommandExecutorTask.executeCommand(CommandExecutorTask.java:112)
at
org.apache.shardingsphere.proxy.frontend.command.CommandExecutorTask.run(CommandExecutorTask.java:78)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
```
### Reason analyze (If you can)
Screenshot:
<img width="1396" alt="图片"
src="https://user-images.githubusercontent.com/42492540/185292016-5a69b4b2-8568-4865-9249-5bb4802806c9.png";>
JDBCBackendStatement could not get databaseType by current databaseName.
### Steps to reproduce the behavior, such as: SQL to execute, sharding rule
configuration, when exception occur etc.
1, Prepare sharding_db and t_order
2, Execute SQL:
```
mysql> use mysql
mysql> select count(1) from sharding_db.t_order;
```
### Example codes for reproduce this issue (such as a github link).
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