询问 [英] query
问题描述
i在我尝试使用公共值从两个表中检索值时遇到问题。
ie
table1有emp_id和name,table2有emp_id和prod ..
i试图使用查询
选择名称,从table1 prod,table2 where table1.emp_id =''some value'' ;
问题是表2中存在数据冗余并使用不同的关键字我也得到了不需要的值。
ie。
select distinct name,prod from table1,table2 where table1.emp_id =''some value'';
i得到了prod的所有值。
我应该使用什么样的查询表中的反向值以避免冗余和不需要的数据。
试试这个:
展开 | 选择 | 换行 | 行号
< blockquote>为了避免JOIN中数据的冗余,你需要通过表名来限定字段名称。
感谢查询它的工作正常。
i面对当我试图知道特定emp_id销售的产品数量时出现问题
即
从t1,t2组t2.id选择t1.name,count(prod) ;
错误不是GROUP BY表达式。
hi,
i faced a problem when i tried to retrive value from two table using a common value.
ie
table1 has emp_id and name,table2 has emp_id and prod..
i tried to use the query
select name,prod from table1,table2 where table1.emp_id=''some value'';
The problem was there was redundancy of data in table2 and using distinct key word also i got unwanted values.
ie.
select distinct name,prod from table1,table2 where table1.emp_id=''some value'';
i got all the values of prod.
what kind of query i should use to retrive value from both the table to avoid redundant and unwanted data.解决方案Try this:
Expand|Select|Wrap|Line Numbers
To avoid redundancy of data in JOIN, you need to qualify the field names by the table name.
Thanks for the query its work fine.
i faced a problem when i tried to know the number of products sold by a particular emp_id
ie
select t1.name,count(prod) from t1,t2 group t2.id;
The error was not a GROUP BY expression.
这篇关于询问的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文