MySQL - complicated LEFT JOIN
I have that one-to-many relationship going here. Plus, not all "primary" records will have a joined record in the second database table.
Here are my tables:
tbl_customers tbl_addresses
A customer record in tbl_customers
can obviously have many addresses, in the tbl_addresses
table.
Here's my dilemma. There are many customer records with several addresses, and I assign one of those address records as the "main" address for a customer record. This is simply a single column
called: primaryAddress
. The value will be a number 1, if that address record is the main address.
So here is my query:
SELECT c.customername, a.state
FROM `tbl_customers` c
LEFT JOIN `tbl_addresses` a ON c.customerid = a.customerid
That query will result 开发者_开发技巧in duplicate records for any customer with more than 1 address. If I add a little more to the LEFT JOIN:
SELECT c.customername, a.state
FROM `tbl_customers` c
LEFT JOIN `tbl_addresses` a ON c.customerid = a.customerid AND a.primaryAddress = 1
This produces no results, even when I see in the database there are plenty of address records with primaryAddress = 1.
So I'm thinking my query is wrong.
Can someone see what I'm missing?
To anyone who happens to land on this page looking for a solution:
THIS DOES NOT PROPERLY ANSWER THE QUESTION
The user was able to find the cause after discussing the problem here. Turns out he had a typo on his original code. The second block of SQL code posted on the question is correct, and should give the expected results. +1 for user JoeStefanelli for pointing this out.
Please read the comments for details. My original answer is below. Now I see I should have deleted it, instead of trying to amend it, as soon I realized it was flawed. At least the discussion helped the user find a solution...
My original answer:
You are almost there. Add
a.primaryAddress = 1
to theWHERE
clause instead.EDIT
Not sure if this will exclude costumers with zero addresses from the results...
精彩评论