在不使用连接的情况下从多个表中检索数据 [英] Retrive data from more than one table without using joins

问题描述

i我有两张桌子..

1）员工表列是EmpId，EmpName，CityId ....

2）城市表列是CityId，CityName ...



现在我想从这两个中获取employeeId，员工姓名，城市名称没有使用连接的表...



是否可能...

解决方案

这是可能的。试试这个

选择a.EmpId，a.EmpName，a.CityId，b.CityId，b.CityName from employeableable as a，citytable as b 

嗯......是的。但这是一个愚蠢的想法！



如果你有两个表之间的链接，那么你可能想要返回一行只与该行相关的数据 - 并且最好的方法是使用 JOIN 。

如果你不返回相关的行：

  SELECT  *  FROM  MyTable，MyTable2 

然后它只能为MyTable的每一行重新输入MyTable2的每一行：所以如果MyTable中有6行，MyTable2中有2行，它将返回12行。



如果您使用联接：

  SELECT  *  FROM  MyTable m1 
  JOIN  MyTable2 m2  ON  m1.ID = m2.Id 

然后它只返回你感兴趣的行。

如果你真的很绝望，你可以在没有加入的情况下这样做：

 < span class =code-keyword> SELECT  *  FROM  MyTable，MyTable2  WHERE  MyTable。 ID = MyTable2.Id 

它将返回相同的行。



在性能方面，没有区别，但是 JOIN 表格更容易维护，特别是如果查询变得更复杂。

良好做法建议 JOIN 超过 WHERE 表格。

访问这里这将有助于你



http ：/ // hlog =http：/ /blog.sqlauthority.com/2008/10/17/sql-server-get-common-records-from-two-tables-without-using-join/target =_ blanktitle =New Window> ^

Hi,

i am having two tables..
1) employee table columns are EmpId,EmpName,CityId....
2) City table columns are CityId,CityName...

Now i want to fetch employeeId,Employee name,cityname from these two tables without using joins...

is it possible ...

解决方案

It is possible.try this

select a.EmpId,a.EmpName,a.CityId,b.CityId,b.CityName from employeetable as a,citytable as b

Well...yes. But it's a stupid idea!

If you have a link between the two tables, then you presumably want to return data on a row that is only relevant to that row - and the best way to do that is with a JOIN.
If you don't return only the relevant rows:

SELECT * FROM MyTable, MyTable2

Then it can only retirn each row of MyTable2 for each row of MyTable: so if you have 6 Rows in MyTable and 2 in MyTable2, the it will return 12 rows.

If you use a join:

SELECT * FROM MyTable m1
JOIN MyTable2 m2 ON m1.ID=m2.Id

Then it returns only the rows you are interested in.
You could do it without a JOIN if you were really desperate:

SELECT * FROM MyTable, MyTable2 WHERE MyTable.ID=MyTable2.Id

And it will return the same rows.

In performance terms, there is no difference, but the JOIN form is a lot easier to maintain, particularly if the query becomes more complex.
Good practice recommends the JOIN over the WHERE form.

visit here this will help you

http://blog.sqlauthority.com/2008/10/17/sql-server-get-common-records-from-two-tables-without-using-join/[^]

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