加入MySQL的LIMIT结果

Question

take the case you have 2 table, for example tbCostumers and tbOrders. I would like to display a summary list with all costumers, related orders and display them with a paginator.

Doing a join I can extract costumers list and all orders for each costumer, the result is something like:

idCostumer | name | ... | idProduct | productName | price | ...

Where the first n columns are all equal if the costumer has more than 1 order. So I can have:

1 | will | ... | 12 | product1 | 123 | ...
2 | bill | ... | 23 | product2 | 321 | ... 
2 | bill | ... | 24 | product3 | 231 | ...

And so on

I'm trying to use LIMIT to extract only n records and using them with a paginator.

First question: if a costumer has more than 1 order, with this query I'll see n records, equal in the first column (id, name, ... and other costumer info) but different at the end, where there are products info. Is this 'correct'? Is there another way to extract this informations?

Second question: if I do that and I use a LIMIT , I could "cut" the result table between 2 (or more) records that represent the same customer; so, for example in the small table above, if I limit with 2 the third row will be lost, even if it's part of the row above, because is just another order of the same costumer.

I would like to limit the number of different idCostumer, in order to take exactly n costumers, even if they appear more than 1 times in the result table. Something like n different idCostumer, no matter if they are repeated.

Is this possible?

I hope it's clear, it was not easy to explain what I would like to achieve :)

Thank you!

Answer 1

You might want to have something like this:

SELECT * FROM (
  (SELECT * FROM tbCustomers LIMIT 3) AS c
  INNER JOIN tbOrders AS o ON o.customer = c.idcustomer 
);

You can substitute the first asterisk with named columns and only receive your desired columns in the order you prefer (ie: SELECT c.name, o.price FROM...) .

Hope this works for you!

EDIT : changing the value of the LIMIT clause changes the number of the picked customers, of course.

EDIT 2 : As Alvaro Pointed out, you'll probably need an order clause in the tbCustomers query.