为什么我的dao层sql语句加％就能读出数据,不加就读取为空呢?

Question

package com.southwind.dao.impl;

import com.southwind.dao.DormitoryAdminDao;
import com.southwind.entity.DormitoryAdmin;
import com.southwind.entity.SystemAdmin;
import com.southwind.util.JDBCUtil;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class DormitoryAdminDaoImpl implements DormitoryAdminDao {


    @Override
    public List<DormitoryAdmin> search(String key, String value) {
        Connection connection = JDBCUtil.getConnection();
        String sql = "select * from bzlist where " + key + " like'%" + value + "%'";
        //String sql = "select * from bzlist where " + key + " like " + value + " ";
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        List<DormitoryAdmin> list = new ArrayList<>();
        try {
            statement = connection.prepareStatement(sql);
            resultSet = statement.executeQuery();
            while (resultSet.next()) {
                String UUID = resultSet.getNString(1);
                String XM = resultSet.getNString(2);
                String SFZ = resultSet.getNString(3);
                String SJHM = resultSet.getNString(4);
                String BYHM = resultSet.getNString(5);
                String YHKH = resultSet.getNString(6);
                String HJSZD = resultSet.getNString(7);
                String JTRKS = resultSet.getNString(8);
                String GZDW = resultSet.getNString(9);
                String THSJ = resultSet.getNString(10);
                String THZT = resultSet.getNString(11);
                String BZ = resultSet.getNString(12);
                String DB = resultSet.getNString(13);
                String CJ = resultSet.getNString(14);
                String JZFP = resultSet.getNString(15);
                String TUJR = resultSet.getNString(16);
                String DW = resultSet.getNString(17);
                String ZWDW = resultSet.getNString(18);
                String BSSJ = resultSet.getNString(19);
                String Colour = resultSet.getNString(20);
                list.add(new DormitoryAdmin(UUID, XM, SFZ, SJHM, BYHM, YHKH, HJSZD, JTRKS, GZDW, THSJ, THZT, BZ, DB, CJ, JZFP, TUJR, DW, ZWDW, BSSJ, Colour));
            }


        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.release(connection, statement, resultSet);
        }
        return list;
    }


    @Override
    public List<DormitoryAdmin> IdSearch(String value) {
        Connection connection = JDBCUtil.getConnection();
        String sql = "select * from bzlist where uuid like  " + value + " ";
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        List<DormitoryAdmin> list = new ArrayList<>();
        try {
            statement = connection.prepareStatement(sql);
            resultSet = statement.executeQuery();
            while (resultSet.next()) {
                String UUID = resultSet.getNString(1);
                String XM = resultSet.getNString(2);
                String SFZ = resultSet.getNString(3);
                String SJHM = resultSet.getNString(4);
                String BYHM = resultSet.getNString(5);
                String YHKH = resultSet.getNString(6);
                String HJSZD = resultSet.getNString(7);
                String JTRKS = resultSet.getNString(8);
                String GZDW = resultSet.getNString(9);
                String THSJ = resultSet.getNString(10);
                String THZT = resultSet.getNString(11);
                String BZ = resultSet.getNString(12);
                String DB = resultSet.getNString(13);
                String CJ = resultSet.getNString(14);
                String JZFP = resultSet.getNString(15);
                String TUJR = resultSet.getNString(16);
                String DW = resultSet.getNString(17);
                String ZWDW = resultSet.getNString(18);
                String BSSJ = resultSet.getNString(19);
                String Colour = resultSet.getNString(20);
                list.add(new DormitoryAdmin(UUID, XM, SFZ, SJHM, BYHM, YHKH, HJSZD, JTRKS, GZDW, THSJ, THZT, BZ, DB, CJ, JZFP, TUJR, DW, ZWDW, BSSJ, Colour));
            }


        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JDBCUtil.release(connection, statement, resultSet);
        }
        return list;
    }
}

Answer 1

你使用like作为模糊查询，先了解其用法吧，用法都不清楚。

一般模糊语句如下：

SELECT 字段 FROM 表 WHERE 某字段 Like 条件

其中,
%：表示任意0个或多个字符。可匹配任意类型和长度的字符，有些情况下若是中文，请使用两个百分号（%%）表示。

比如 SELECT * FROM [user] WHERE u_name LIKE '%三%'
将会把u_name为“张三”，“张猫三”、“三脚猫”，“唐三藏”等等有“三”的记录全找出来。