与主键和外键有关的ADO查询表的问题 [英] Problem with ADO quering tables related with primary+foreign key

问题描述

大家好！

我参与了一个涉及动态SQL使用的项目，结果出现了问题.

简单的查询，联接，更改和其他工作都很好，但这是问题所在:

假设我有2个表，这些表通过主+外键关联.
让我将它们分别设为表A和表B.

键入SQL查询后，从A，B中选择data_from_A，data_from_B;"我从两个表中得到数据的笛卡尔积.

要进一步阐明:

假设表A保留姓名，表B保留薪水.
一旦开始上述查询，我​​应该得到以下内容:

亚历克斯| 1000
最高| 2000
.
.
.

但我得到了:

亚历克斯| 1000
亚历克斯| 2000
最高| 1000
最高| 2000
.
.
.

等等.

任何参考/代码示例都将受到高度赞赏.

我使用C ++，并且使用过ADO.





与教授讨论后，我们确定他做错了，因为我打字时没有认真注意.
因此，nv3建议的解决方案是唯一可能的方法.
因此，请按照回答关闭此线程.
再次感谢nv3！

Hello,everyone!

I have worked on a project which involves dynamic SQL usage, and there came out an issue.

Simple queries,joins,alter and stuff work well,but this is the issue:

Let us say I have 2 tables,related via primary+foreign key.
Let me dim them as table A and table B.

Once I type SQL query "select data_from_A,data_from_B from A,B;" I get cartesian product of data from both tables.

To clarify even more:

Lets say table A holds names,and table B their salaries.
Once the above query is started I should get the following:

Alex | 1000
Max | 2000
.
.
.

yet I get:

Alex | 1000
Alex | 2000
Max | 1000
Max | 2000
.
.
.

and so on.

Any reference/code example is highly appreciated.

I worked in C++, and have used ADO.





After discussion with professor,we have determined that he made mistake,since he didn''t pay attention carefully when I was typing.
Thus,the solution suggested by nv3 is the only possible way.
Therefore I close this thread as answered.
THANKS AGAIN nv3!

推荐答案

您应该在SQL语句中添加一个where子句，例如

You should put a where-clause in your SQL statement, like

... WHERE B.name = A.name ...

从笛卡尔乘积中仅选择与逻辑上链接表的键相关的那些元组.

to select only those tuples from the cartesian product that match regarding the key that links the tables logically.

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