java怎么查询数据库,数据,数据库,条件,数据表,方法

java怎么查询数据库

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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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