java怎么查询数据库

java查询数据库的方法：首先创建user和teacher数据库；然后将teacher表的【user_id】列与user表的id列建立一对多连接；接着向user数据表中添加数据，并按照条件查询user数据库数据；最后根据主表查询从表数据。

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java查询数据库的方法：

一、创建数据库

创建 user 数据库

创建 teacher 数据库

teacher表的user_id列与user表的id列建立一对多连接，user_id作为外键。

二、Java编程查询数据库

向user数据表中添加数据

    /**      * 添加数据      */     @Test     public void addData() {         Connection connection = null;         PreparedStatement pstmt =null;         try {             connection = JDBCUtils_V3.getConnection();             String sql = "insert into user values(null,?,?)";             pstmt = connection.prepareStatement(sql);             pstmt.setString(1, "wangxuan");             pstmt.setString(2, "741852");             int row = pstmt.executeUpdate();             if (row>0) {                 System.out.println("数据添加成功！");             }else {                 System.out.println("数据添加失败！");             }         } catch (SQLException e) {             // TODO Auto-generated catch block             e.printStackTrace();         }finally{             JDBCUtils_V3.release(connection, pstmt, null);         }     }

按照条件查询user数据库数据

    /**      * 按照条件查询数据      */     @Test     public void selectTest() {         Connection conn = null;         PreparedStatement pstmt = null;         ResultSet rs =null;         try {             conn = JDBCUtils_V3.getConnection();             String sql = "select * from user where password = ?";             pstmt = conn.prepareStatement(sql);             pstmt.setString(1, "123456");             rs = pstmt.executeQuery();             while (rs.next()) {                 System.out.println(rs.getString(1)+"----"+rs.getString(2)+"---"+rs.getString(3));             } //            System.out.println(rs);         } catch (SQLException e) {             // TODO Auto-generated catch block             e.printStackTrace();         }finally{             JDBCUtils_V3.release(conn, pstmt, rs);         }     }

一对多查询/根据主表user查询从表teacher数据

    /**      * 一对多查询      * 根据主表查询从表      */     @Test     public void selectOnetoMore() {         Connection conn = null;         PreparedStatement pstmt = null;         ResultSet rs = null;         try {             conn = JDBCUtils_V3.getConnection(); //            String sql = "select * from teacher where user_id = (select id from user where username =?) ";             String sql = "select * from user,teacher where user.id = teacher.user_id ";             pstmt = conn.prepareStatement(sql); //            pstmt.setString(1, "wangxuan");             rs = pstmt.executeQuery();             while (rs.next()) { //                System.out.println(rs.getString(1)+"----"+rs.getString(2)+"---"+rs.getString(3)+"---"+rs.getString(4));                 System.out.println(rs.getString(1)+"----"+rs.getString(2)+"---"+rs.getString(3)+"---"+rs.getString(4)+"----"+rs.getString(5)+"----"+rs.getString(6)+"----"+rs.getString(7));             }             System.out.println("查询完成");         } catch (SQLException e) {             // TODO Auto-generated catch block             e.printStackTrace();         }finally{             JDBCUtils_V3.release(conn, pstmt, rs);         }     }

一对多查询/根据从表查询主表

    /**      * 一对多查询      * 根据从表查询主表数据      */     @Test     public void selectMoretoOne() {         Connection connection = null;         PreparedStatement pstmtPreparedStatement = null;         ResultSet rSet =null;         try {             connection = JDBCUtils_V3.getConnection();             String sql = "select * from user where id = (select user_id from teacher where teacher=?)";             pstmtPreparedStatement = connection.prepareStatement(sql);             pstmtPreparedStatement.setString(1, "钱田");             rSet = pstmtPreparedStatement.executeQuery();             while (rSet.next()) {                 System.out.println(rSet.getString(1)+"----"+rSet.getString(2)+"---"+rSet.getString(3));             }         } catch (SQLException e) {             // TODO Auto-generated catch block             e.printStackTrace();         }finally{             JDBCUtils_V3.release(connection, pstmtPreparedStatement, rSet);         }     } }

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