Question

Ok, I have an example table with the following information and query.
First up is the data, with the question following at the end.

Here’s the SQL Dump:
http://pastie.org/private/o7zzajdpm6lzcbqrjolgg

Or you can use the included a visual below:

Purchases Table

|  id   |   brand   |    date     |

    1        b1       2000-01-01 
    2        b1       2000-01-03 
    3        b2       2000-01-04
    4        b3       2000-01-08
    5        b4       2000-01-14

Owners Table

id | firstname | lastname | purchaseid | itemCoupon | itemReturned | Accessories
 1     Jane        Doe          1           yes           no               4
 2     Jane        Doe          2           yes           no               2 
 3     Jane        Doe          3           no            no               1
 4     Jane        Doe          4           no            no               3
 5     Jane        Doe          5           no            yes              6

The Query

SELECT brand, COALESCE( SUM( inTime.Accessories ) , 0 ) AS acessory_sum
FROM purchases
INNER JOIN owners AS person ON person.purchaseid = purchases.id
AND person.firstname =  'Jane'
AND person.lastname =  'Doe'
LEFT JOIN owners AS inTime ON person.id = inTime.id
AND purchases.date
BETWEEN DATE(  '2000-01-01' ) 
AND DATE(  '2000-01-05' ) 
GROUP BY purchases.brand

This gives the following expected result:

| brand | accessory_sum
   b1          6
   b2          1
   b3          0
   b4          0

The question

Now, I would like to add to the query:

WHERE itemCoupon = 'yes' OR itemReturned = 'yes'

But this overrides the last join and when I do the same search above I get:

| brand | accessory_sum
   b1          6
   b2          1

Similarly I still want it to return No results found for 2000-01-04, 2000-01-08 using WHERE itemCoupon = 'yes' OR itemReturned = 'yes'. Removing the WHERE gives me zeros for all brands if I try to do it another way.

Basically I want to keep the way the WHERE behaves but also keep the format that I described in the first example of the expected output.

As it is now, using WHERE destroys the way the last LEFT JOIN works with COALESCE which fills the remaining brand rows with zeros.

Answer 1

Your WHERE turns the outer join into an inner join.

You need to move your additionally condition into the LEFT JOIN condition:

LEFT JOIN owners as inTime 
       ON person.id = inTime.id 
      AND purchases.date between purchases.date DATE ('2000-01-01') and DATE ('2000-01-05')
      AND (inTime.itemCoupon = 'yes' or inTime.itemReturned = 'yes')