很多時候需要查詢兩張表及以上的表來獲取需要的資訊

  一張表的時候查詢語句：

             select  列1,列2 from  表 where 查詢條件

      例如：一張表

          查詢一張表中的資料 

             select username, age from 資訊表 where username="王麻子"

             查詢出來的結果                                                          

       兩個表的時候查詢語句

         ①    select 表1.列1, 表1.列2,表2.列1 from 表1,表2 where 表1.列x=表2.列x

         還有另一張表

           用這兩個表查使用者名稱和所使用的武器

           ①   select LOL.user ,LOLp.wuqi from LOL,LOLp where LOL.user_id=LOLp.user_id

          這樣的結果就是

          ②  select   LOL.user ,LOLp.wuqi from LOL left join LOLp on LOL.user_id=LOLp.user_id  where 篩選條件（在不需要篩選條件的時候沒有where語句）

 其他的查詢方式：

SELECT  
distinct
a.userId,a.tijianhao,a.SURVEYID,
a.tbrq as rq,
convert(varchar(10),a.tbrq,120) as tbrq,
a.tijianhao as TJH,
isViewed,
b.jieguo as name, //這裡可以修改正（select jieguo from where tijianhao=a.tijianhao and xmcode="name"）name,
b.flag as TYPE,
a.has_survey 
FROM SHANGWURECORD a
left join ShangWuJieGuo b on a.tijianhao=b.tijianhao and b.xmcode='name'
where a.SURVEYID !='' and a.userid='1234567898763' and belong_id='1234567898763

//比如  帶有別名的

SELECT  
distinct
a.userId,a.tijianhao,a.SURVEYID,
a.tbrq as rq,
convert(varchar(10),a.tbrq,120) as tbrq,
a.tijianhao as TJH,
isViewed,
（select jieguo from where tijianhao=a.tijianhao and xmcode="name"）name,//剛才修改的地方
b.flag as TYPE,
a.has_survey 
FROM SHANGWURECORD a
left join ShangWuJieGuo b on a.tijianhao=b.tijianhao //還有這裡的變化
where a.SURVEYID !='' and a.userid='440Y98F1DQX8' and belong_id='440Y98F1DQX8' order by a.tbrq desc 

第①中一樣的 很重複的表名還是用上面整個別名比較好

select distinct SHANGWURECORD.userId,

SHANGWURECORD.tijianhao,

SHANGWURECORD.SURVEYID,

SHANGWURECORD.tbrq as rq,

convert(varchar(10),SHANGWURECORD.tbrq,120) as tbrq,

isViewed,
ShangWuJieGuo.jieguo as name,

ShangWuJieGuo.flag as TYPE,

SHANGWURECORD.has_survey

 from SHANGWURECORD,ShangWuJieGuo 

where SHANGWURECORD.tijianhao=ShangWuJieGuo.tijianhao 

and SHANGWURECORD.userid='440Y98F1DQX8' and belong_id='440Y98F1DQX8' and ShangWuJieGuo.xmcode='name'