JDBC增删改

以你之姓@ 2022-05-14 06:07 238阅读 0赞

**执行新增操作**

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 <td style="vertical-align:top;width:410.35pt;"> public&nbsp;static&nbsp;void&nbsp;main(String[] args) { &nbsp;add_subject("dba", 12, 4); } &nbsp; /** &nbsp;* 新增科目 &nbsp;* @return&nbsp;&nbsp;0 新增失败 其他新增成功 &nbsp;*/ public&nbsp;static&nbsp;int&nbsp;&nbsp;add_subject(String &nbsp;subjectname,int&nbsp;hour,int&nbsp;gradeid) { int&nbsp;num=0; PreparedStatement ps=null; //每次在java中编写sql&nbsp;请先在navicate中将 sql语句写好 运行无问题再copy //1.编写sql //参数用?代替 不管什么类型 ?都不需要加 '' String &nbsp;sql="insert into `subject` values(NULL,?,?,?)"; //获取执行对象 &nbsp;&nbsp;&nbsp;&nbsp;try&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;ps= connection.prepareStatement(sql); &nbsp;&nbsp;&nbsp;&nbsp; //给参数赋值 &nbsp; &nbsp;&nbsp;&nbsp;&nbsp; //parameterIndex参数索引 &nbsp;jdbc操作的时候 索引都是从1开始 &nbsp;&nbsp;&nbsp;&nbsp; ps.setObject(1, subjectname); &nbsp;&nbsp;&nbsp;&nbsp; ps.setObject(2, hour); &nbsp;&nbsp;&nbsp;&nbsp; ps.setObject(3, gradeid); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp; //执行新增操作 &nbsp;&nbsp;&nbsp;&nbsp; //execute执行 &nbsp;Query查询 &nbsp;executeQuery()--》执行查询操作 &nbsp;executeUpdate()--&gt;执行更新操作(增删改) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;num= &nbsp;&nbsp;ps.executeUpdate(); &nbsp;&nbsp;&nbsp;&nbsp; } catch&nbsp;(SQLException e) { // TODO&nbsp;Auto-generated catch block e.printStackTrace(); }finally&nbsp;{ //先创建后关闭 后创建先关闭 try&nbsp;{ ps.close(); //连接对象 //connection.close(); } catch&nbsp;(SQLException e) { // TODO&nbsp;Auto-generated catch block e.printStackTrace(); } &nbsp; } &nbsp; &nbsp; return&nbsp;&nbsp;num; } </td> 
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**删除操作(根据主键删除)**

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 <td style="vertical-align:top;width:410.35pt;"> public&nbsp;static&nbsp;void&nbsp;main(String[] args) { // add_subject("dba", 12, 4); deletebyid("16"); } /** &nbsp;* 删除 &nbsp;* @param&nbsp;id 科目id &nbsp;* @return&nbsp;&nbsp;0删除失败 &nbsp;其他删除成功 &nbsp;*/ public&nbsp;static&nbsp;int&nbsp;deletebyid(String id) { int&nbsp;num=0; &nbsp; //sql语句 String sql="delete &nbsp;from `subject` where SubjectId=?"; //执行对象是根据sql语句来的 所以每次需要重新获取执行对象 PreparedStatement &nbsp;&nbsp;ps=null; &nbsp;&nbsp;&nbsp;try&nbsp;{ ps= connection.prepareStatement(sql); //给sql的参数赋值 ps.setObject(1, id); //执行删除操作 num= ps.executeUpdate(); if&nbsp;(num&gt;0) { System.out.println("删除成功"); }else&nbsp;{ System.out.println("系统正忙........"); } &nbsp; } catch&nbsp;(SQLException e) { // TODO&nbsp;Auto-generated catch block e.printStackTrace(); }finally&nbsp;{ try&nbsp;{ ps.close(); } catch&nbsp;(SQLException e) { // TODO&nbsp;Auto-generated catch block e.printStackTrace(); } } &nbsp; return&nbsp;num; &nbsp; } </td> 
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**修改(在后续修改的操作一般都是通过主键来完成)**

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 <td style="vertical-align:top;width:410.35pt;"> public&nbsp;static&nbsp;void&nbsp;main(String[] args) { // add_subject("dba", 12, 4); //deletebyid("16"); update_subject("啊啊啊啊", 15, 44, 2); &nbsp; } &nbsp; public&nbsp;static&nbsp;int&nbsp;update_subject(String subjectname, int&nbsp;subjectid, int&nbsp;hour, int&nbsp;gradeid) { int&nbsp;num&nbsp;= 0; String sql&nbsp;= "update `subject` set SubjectName=?,ClassHour=?, GradeId=? where SubjectId=?"; // 执 PreparedStatement ps&nbsp;= null; &nbsp; try&nbsp;{ ps&nbsp;= connection.prepareStatement(sql); // 给sql的参数赋值 参数 1,2代表的是sql中第几个?号 ps.setObject(1, subjectname); ps.setObject(2, hour); ps.setObject(3, gradeid); ps.setObject(4, subjectid); num&nbsp;= ps.executeUpdate(); if&nbsp;(num&nbsp;&gt; 0) { System.out.println("修改成功"); } else&nbsp;{ System.out.println("未知错误...."); } } catch&nbsp;(SQLException e) { // TODO&nbsp;Auto-generated catch block e.printStackTrace(); }finally&nbsp;{ try&nbsp;{ ps.close(); } catch&nbsp;(SQLException e) { // TODO&nbsp;Auto-generated catch block e.printStackTrace(); } } &nbsp; return&nbsp;num; } </td> 
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