新建一个测试用的数据库jdbctest
create database if not exists jdbctest default character set 'utf8'; use jdbctest; create table if not exists user( uid int unsigned auto_increment key, username varchar(20) not null, password varchar(20) not null, name varchar(20) not null )engine=innodb charset=utf8; insert user values (null, 'aaa', '111', '张三'), (null, 'bbb', '222', '李四'), (null, 'ccc', '333', '王五');
下载数据库驱动并导入到jdbc项目
下载地址:https://mvnrepository.com/artifact/mysql/mysql-connector-java
编写jdbc测试程序(mysql版本为8.0.17)
package demo1; import java.sql.connection; import java.sql.drivermanager; import java.sql.resultset; import java.sql.sqlexception; import java.sql.statement; import org.junit.test; public class jdbcdemo1 { @test /** * jdbc入门程序 */ public void demo1() { connection conn = null; statement stmt = null; resultset rs = null; try { //1.加载驱动 class.forname("com.mysql.cj.jdbc.driver"); //2.获得连接 conn = drivermanager.getconnection("jdbc:mysql://localhost:3306/jdbctest" + "?usessl=false&servertimezone=hongkong&useunicode=true&characterencoding=utf-8", "root", "1234"); //3创建执行sql语句的对象,并且执行sql //3.1创建执行sql语句的对象 string sql = "select * from user"; stmt = conn.createstatement(); //3.2执行sql rs = stmt.executequery(sql); while(rs.next()) { int uid = rs.getint("uid"); string username = rs.getstring("username"); string password = rs.getstring("password"); string name = rs.getstring("name"); system.out.println(uid + "-" + username + "-" + password + "-" + name); } } catch (sqlexception | classnotfoundexception e) { e.printstacktrace(); } finally { //4.释放资源 if(rs != null) { try { rs.close(); } catch (sqlexception sqlex) { // ignore } rs = null; } if(stmt != null) { try { stmt.close(); } catch (sqlexception sqlex) { // ignore } stmt = null; } if(conn != null) { try { conn.close(); } catch (sqlexception sqlex) { // ignore } conn = null; //垃圾回收机制更早回收对象。 } } } }
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MySQL-关系代数-并、交、差、等值连接、自然连接、左连接。。。
【MySQL牛客】10.获取所有非manager的员工emp_no
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