[Phpmyadmin-devel] RFE #1491

[Marc Delisle]

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

-- 
Marc Delisle | phpMyAdmin