Java.sql.SQLException:Can not issue empty query.

1. Description of false narrative

java.sql.SQLException: Can not issue empty query.
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:996)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:935)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:924)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:870)
	at com.mysql.jdbc.StatementImpl.checkNullOrEmptyQuery(StatementImpl.java:492)
	at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1367)
	at com.you.sql.Student.queryStudent(Student.java:51)
	at com.you.sql.Student.main(Student.java:79)

2. Cause of error

/**
 *
 * @Project:MySQL
 * @Title:Student.java
 * @Package:com.you.sql
 * @Description:
 * @Author:YouHaiDong
 * @Date: June 10, 2015 11:49:36 PM
 * @Version:
 */
Package com.you.sql;

Import java.sql.Connection;
Import java.sql.DriverManager;
Import java.sql.ResultSet;
Import java.sql.SQLException;
Import java.sql.Statement;


/**
 * <p>Please summarize the function in one sentence</p>
 * @ClassName:Student
 * @Description:
 * @Author:YouHaiDong
 * @Date: June 10, 2015 11:49:36 PM
 *
 */
Public class Student
{
/**
* Query student basic information
* @Title:Student
* @Description:
* @Date: June 11, 2015 12:06:40 AM
* @return :void
* @throws
*/
Public static void queryStudent()
{
StringBuffer sql = new StringBuffer();
String url = "jdbc:mysql://localhost:3333/student";
String user = "root";
String password = "root";
Connection conn = null;
Statement stat = null;
ResultSet rs = null;
Try
{
Conn = DriverManager.getConnection(url, user, password);
Stat = conn.createStatement();
Rs = stat.executeQuery(sql.toString());
While(rs.next())
{
String stuId = rs.getString("stu_id");
String stuName = rs.getString("stu_name");
String stuSex = rs.getString("sex");
String stuAge = rs.getString("stu_age");
String stuPhone = rs.getString("stu_phone");
System.out.println("student number:"+stuId+"----"+" Name: "+stuName+"----"+" Gender: "+stuSex+"---"+" Age: "+ stuAge+"----"+"Phone: "+stuPhone";
}
}
Catch (SQLException e)
{
e.printStackTrace();
}
}

/**
*
* @Title:Student
* @Description:
* @param args
* @Date: June 11, 2015 12:07:53 AM
* @return :void
* @throws
*/
Public static void main(String args[])
{
queryStudent();
}
}

3, the solution of the method

SQL is empty because it is running RS = Stat.executequery (sql.tostring ()); Cause an error

StringBuffer sql = new StringBuffer ();
Sql.append ("SELECT * from T_stu_info");

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Java.sql.SQLException:Can not issue empty query.