我有两个表,要从里面提取出内容并显示。
方法1:会出现错误:string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote,toupiao_choose choose where vote.vid=choose.vid";方法2:没问题string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote,toupiao_choose choose where vote.vid=choose.vid";我想问这两种语句有什么区别吗?什么时候能用方法1,什么时候必须用方法2呢?
方法1:会出现错误:string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote,toupiao_choose choose where vote.vid=choose.vid";方法2:没问题string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote,toupiao_choose choose where vote.vid=choose.vid";我想问这两种语句有什么区别吗?什么时候能用方法1,什么时候必须用方法2呢?
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string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote,toupiao_choose choose where vote.vid=choose.vid";不知同样的查询语句
会报什么错误?
方法1:会出现错误:string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote,toupiao_choose choose where vote.vid=choose.vid";方法2:没问题string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote left join toupiao_choose choose on vote.vid=choose.vid group by vote.vid ,vote.vtitle,vote.vendtime,choose.vid ";
我想问这两种语句有什么区别吗?什么时候能用方法1,什么时候必须用方法2呢?
string sqlstr = "select vote.vid, vote.vtitle,vote.vendtime,sum(choose.cpiaoshu) as zongshu,choose.vid from toupiao_vote vote left join toupiao_choose choose on vote.vid=choose.vid group by vote.vid ,vote.vtitle,vote.vendtime,choose.vid "
用聚合函数要分组吗?