Re: [Phpmyadmin-devel] RFE #1491

On Sat, Aug 2, 2014 at 5:28 PM, Marc Delisle marc@infomarc.info wrote:

Le 2014-08-02 06:42, Ashutosh Dhundhara a écrit :

...

On Sat, Aug 2, 2014 at 2:45 AM, Marc Delisle <marc@infomarc.info mailto:marc@infomarc.info> wrote:

Le 2014-08-01 16:32, Ashutosh Dhundhara a écrit :
> Hi all,
>
> I was looking into RFE #1491
> <http://sourceforge.net/p/phpmyadmin/feature-requests/1491/>

(Support

...

> InnoDB for database Query by example). If I am not wrong, is the
concept
> of displaying the 'LEFT JOIN' is something like as discussed in
the case
> below:
>
> Lets say I have two tables:
>
> CREATE TABLE `product` (
>  `id` int(11) NOT NULL,
>  `price` decimal(10,0) DEFAULT NULL,
>  PRIMARY KEY (`id`)
> )
>
> CREATE TABLE `product_order` (
>  `product_id` int(11) NOT NULL,
>  `customer_id` int(11) NOT NULL,
>  KEY `product_category` (`product_id`),
>  KEY `customer_id` (`customer_id`),
>  CONSTRAINT `product_order_ibfk_4` FOREIGN KEY (`product_id`)
REFERENCES
> `product` (`id`)
> )
>
> Now in QBE interface, when I will select
`product_order`.`product_id` in
> first column drop-down and `product`.`id` in second column
drop-down, I
> should get the following result:
>
> FROM `db_name`.`product_order` LEFT JOIN `db_name`.`product`
> ON `product_order`.`product_id` = `product`.`id`
>
> In general, 'LEFT JOIN' with foreign table and ON condition between
> master column and foreign column. Am I getting it right?

Hi Ashutosh,

For the record, you are using the example given in [0].

Note that to make a more complete example, you have to click
the Show checkboxes for each selected column. Also, you would have to
choose another column, for example the price. When the feature is
implemented, as per your suggestion this would generate:

select `product`.`price`, `product_order`.`product_id`,

`product`.`id`

...

FROM `product_order` LEFT JOIN `product` ON

`product_order`.`product_id`

...

= `product`.`id`

Now, choosing which table is on which side of the LEFT JOIN is open

to

...

interpretation.

The current QBE interface does not permit to specify which table
you want on the left side and it's a shortcoming. It's not clear if
the user wants to show all of the products, even those for which
there are no order. If this is the case, it should become

FROM `product` LEFT JOIN `product_order` ...

I tend to think that this is what the user wants. So, this is the
statement we should aim for:

select `product`.`price`, `product_order`.`product_id`,

`product`.`id`

...

FROM `product` LEFT JOIN `product_order` ON

`product_order`.`product_id`

...

= `product`.`id`

producing results such as:

price   product_id      id
100     10              10
2000    20              20
3000    NULL            30

where there is no order for product id 30.

I'm not sure whether we should let the user decide which table

should be

...

on the left side. Things can become tricky in the UI when you add a
third table like customer.

[0]

http://dev.mysql.com/doc/refman/5.6/en/create-table-foreign-keys.html

...

Thanks Marc,

That was quite comprehensive description of the problem. I also think that user generally want to display (in context with above example) all the products, even those for which there are no order. So in that case following statement becomes our objective:

SELECT `product`.`price`, `product_order`.`product_id`, `product`.`id` FROM `product` LEFT JOIN `product_order` ON `product_order`.`product_id` = `product`.`id`

But if we talk about the current scenario, in case of 'Internal relations', the QBE generates the following statement:

SELECT `product`.`price`, `product_order`.`product_id`, `product`.`id` FROM `product_order` LEFT JOIN `product` ON `product_order`.`product_id` = `product`.`id`

I selected `product`.`price`, `product_order`.`product_id` and `product`.`id` in columns 1, 2 and 3 respectively with 'Show' checkboxes checked. And I have an internal relation defined from `product_order`.`product_id` to `product`.`id`. I am a little confused here. Am I doing something wrong?

This is the current behavior of QBE for internal relations. In libraries/DBQbe.class.php, if you look for "LEFT JOIN", you'll find what is the logic used.

So much the better if this logic can be improved when doing your task with InnoDB. If not, we can leave the logic for internal relations as it is currently.

Thanks Marc.

I tried to improve the current logic for internal relations as suggested by you. It works fine for my test cases. Can you point me to some more complex test cases for this or should I create a pull request?