sql in תΪexists

-- MySQL dump 10.10
--
-- Host: localhost Database: test
-- ------------------------------------------------------
-- Server version 5.0.22-community-nt
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
--
-- Table structure for table `student`
--
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
`id` int(11) default NULL,
`t_id` int(11) default NULL,
`name` varchar(255) default NULL
) ENGINE=InnoDB DEFAULT CHARSET=gbk;
--
-- Dumping data for table `student`
--
/*!40000 ALTER TABLE `student` DISABLE KEYS */;
LOCK TABLES `student` WRITE;
INSERT INTO `student` VALUES (1,1,'s1'),(2,1,'s2'),(3,1,'s3'),(4,2,'s44'),(5,2,'s55'),(6,2,'s6');
UNLOCK TABLES;
/*!40000 ALTER TABLE `student` ENABLE KEYS */;
--
-- Table structure for table `teacher`
--
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
`id` int(11) default NULL,
`name` varchar(255) default NULL
) ENGINE=InnoDB DEFAULT CHARSET=gbk;
--
-- Dumping data for table `teacher`
--
/*!40000 ALTER TABLE `teacher` DISABLE KEYS */;
LOCK TABLES `teacher` WRITE;
INSERT INTO `teacher` VALUES (1,'t1'),(2,'t2'),(3,'t3');
UNLOCK TABLES;
/*!40000 ALTER TABLE `teacher` ENABLE KEYS */;
/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;
/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET