Hi Arthur,
Thanks for your answer and your example. Your example is very good but I
can't map to what I'm trying to do. As you suggested I have to
understand how inner join is implemented in MySQL. The query that I'm
working on selects fields from three tables, in this way,
Table_1 has columns A,B,C supplies fields ( A,B, C)
Table_2 has columns A,T,U supplies fields (T,U)
Table_3 has columns A,B,C,X,Y,Z supplies fields (X,Y,Z)
Table_1 and table_2 have a strange relationship with each other, one row
in table_3 could match with a number of rows in table_1 if table_1.A =
table_3.A and table_1.B=table_3.B and (table_1.C=table_3.C or table_3.C
= "*"). That's what I can't get to work.
I worked on this on MSSQL and wrote a query that does the above but I
cannot find the equivalent query for it in MySQL.
For I've split the query in two parts and put the results back together
in my application. But I would look at DBTools and see if I can learn
something from it.
Thanks again for you advice.
[EMAIL PROTECTED] wrote:
> Once you understand the logic of joins the rest is pretty straightforward,
> since in terms of execution the sequence in which you do the joins is
> irrelevant. (Performance is another issue, quickly resolved by specifying
> the smallest tables first.)
>
> Supposing that you have tables Products, Suppliers and Categories, which
> Products having foreign keys referencing Suppliers and Categories...
>
> SELECT ProductID, ProductName, SupplierID, SupplierName, CategoryID,
> CategoryName
> FROM Products INNER JOIN Suppliers ON Products.SupplierID =
> Suppliers.SupplierID
> INNER JOIN Categories ON Products.CategoryID = Categories.CategoryID;
>
> You can just keep building up such a query according to the number of tables
> you need to drag into the operation. Given the above query, you may well
> want to change the order of table references, but that doesn't intrude upon
> the logic and unless you have a very large number of rows in one or more
> tables, the performance difference will barely be noticeable.
>
> There are several GUI tools that let you perform multi-table selects using
> drag-and-drop techniques (c.f. DBTools, IMO one of the finest, with the
> added benefit that it remembers relatinships that you declare within it).
> Then you can inspect the code it writes and tweak it to suit using EXPLAIN.
>
> hth,
> Arthur
>
> ----- Original Message -----
> From: "damovand" <[EMAIL PROTECTED]>
> To: "mysql" <[EMAIL PROTECTED]>
> Sent: Thursday, October 03, 2002 12:31 PM
> Subject: Is there Examples and Documents on joining tables?
>
>
>
>>Is there a document that compiles examples on different ways of joining
>>two or more tables? I found a few on
>>http://www.mysql.com/doc/en/JOIN.html but they do not cover joining more
>>than two tables.
>>
>>Thanks for any suggestions.
>>
>>
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