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yuqinchuan 11 posts Joined 05/08
29 May 2008
What is the meaning of the implicit join?

What is the meaning of the implicit join?Please give me an example,thank you very much?

Roddy 3 posts Joined 07/07
29 May 2008

I think the following illustrates an implicit join:...FROM T1INNER JOIN T2 ON T1.A = T2.BINNER JOINN T3 ON T2.B = T3.C...The above has the following implied joinINNER JOIN T3 ON T1.A = T3.Cas T1.A is already proven to be joined to T2.BPlease correct me if I'm wrong.

SN 77 posts Joined 01/07
29 May 2008

hi,Implicit join is where no join keyword is mentioned explicitly. for example,select........from T1, T2........ ;is an implicit join where no JOIN keyword is mentioned explicitely and depends on the WHERE condition, if specified.below is an exmaple for explicit join:select........from T1 left outer join T2 on T1.col1=T2.col1........ ;

Adeel Chaudhry 773 posts Joined 04/08
29 May 2008

Hello,Implicit join is the join without explicitly writting the word JOIN of any kind (inner, outer, left...). Following is the example of implicit join, it is always a cross-join:SELECT a.col1, b.col1FROM table1 a, table2 b;The example given by Roddy is a simple inner join.Regards,Adeel

-- If you are stuck at something .... consider it an opportunity to think anew.

Adeel Chaudhry 773 posts Joined 04/08
29 May 2008

Additionally, if you want to have implicit inner join you can write the query as follows:SELECT a.col1, b.col1FROM table1 a, table2 bWHERE a.col1 = b.col1;HTH.Regards,Adeel

-- If you are stuck at something .... consider it an opportunity to think anew.

yuqinchuan 11 posts Joined 05/08
31 May 2008

But I found that the following example is an implicit join,and have inner join in this example,please tell me why?select * from t1 inner join t2 on t1.a1=t2.a2,t3 where t1.b1=t3.b3

Adeel Chaudhry 773 posts Joined 04/08
01 Jun 2008

You found pretty right.SELECT * FROM t1 INNER JOIN t2 ON t1.a1=t2.a2 ,t3 WHERE t1.b1=t3.b3It uses three tables whish are t1, t2 and t3. t1 is INNER JOINED with t2, this joined table is then IMPLICITLY JOINED (comma between join condition and t3) with table t3.Regards,Adeel

-- If you are stuck at something .... consider it an opportunity to think anew.

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