小编Rag*_*ghu的帖子

我有一张桌子Business_Unit:

    business_unit_id    int
    area_code           nvarchar(100)
    region_code         nvarchar(100)
    sub_region_code     nvarchar(100)

它有一些价值.

查询1:

select 
    business_unit_id,* 
from 
    business_unit 
order by 
    business_unit_id desc

当我查询这个时,我收到以下错误.

消息209,级别16,状态1,行1
不明确的列名称'business_unit_id'.

为了解决这个问题,我使用了表的别名作为bu,并在列中添加了别名作为前缀.

select 
    bu.business_unit_id, * 
from 
    business_unit bu 
order by 
    bu.business_unit_id desc

即使以下查询也可以.

select 
    bu.business_unit_id, bu.* 
from 
    business_unit bu 
order by 
    bu.business_unit_id desc

我想知道,为什么它抛出错误[business_unit_id],查询"查询1".这里没有歧义,我只有一张桌子.

你可以解释吗？

问这个问题的原因.我有一个120列表(假设bigtable),现在,我想通过说90列来命令它.我无法滚动并检查值,因此我将选择90thcolumn,*从bigtable order by 90thcolumn.

我有一个公司实体对象列表。

package com.raghu.example2;
    public class CompanyEntity {

        private String name;

        private String locationName;

        private String officeName;

        private String buildingName;


        public CompanyEntity(String name, String locationName, String officeName, String buildingName) {
            super();
            this.name = name;
            this.locationName = locationName;
            this.officeName = officeName;
            this.buildingName = buildingName;
    //      System.out.println(this);
        }

        public String getName() {
            return name;
        }

        public String getLocationName() {
            return locationName;
        }

        public String getOfficeName() {
            return officeName;
        }

        public String getBuildingName() {
            return buildingName;
        }

        @Override
        public String toString() {
            StringBuilder builder …

我是java 8的新手并且学习lambda表达式.

我有一个界面.

Configuration.java

package com.raghu.example;

import java.util.Map;


public interface Configuration {

    public Map<String,String> getPayload();

}

Impl用于接口:ConfigurationImpl.java

package com.raghu.example;

import java.util.HashMap;
import java.util.Map;

public class ConfigurationImpl implements Configuration {

    @Override
    public Map<String, String> getPayload() {
        Map<String,String> map = new HashMap<>();
        map.put("key1", "value1");
        map.put("key2", "value2");
        //return null;
        return map;
    }

}

我的主程序:Sample.java

package com.raghu.example;
import java.util.Optional;

public class Sample {

    Configuration config;

    /*
     * if config is null, return "";
     * if config.getPaylaod is null, return "";
     * if config.payload is …