How would I write this SELECT statement?

Posted on 2016-08-23
Last Modified: 2016-08-24
Here's what I've got in my table right now. Take note of the DISTINCT door_id's (389, 287)

shopping cart
I've got another table called doors. Each door id has a corresponding "feature_door_name." I need to write a SELECT statement that starts off with something like this:

select DISTINCT door_id from cart where session_id='i2rnvaoealphebajh9e0jsipb7'

..and do a JOIN of some kind that allows me to retrieve the feature_door_name. That data looks like this:

What do you think?
Question by:brucegust
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LVL 41

Expert Comment

ID: 41767984
Either INNER or LEFT JOIN, based on your requirement.

SELECT t1.*, c.feature_door_name
   FROM your_table t1
   JOIN cart c ON t1.door_id = c.door_id

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SELECT t1.*, c.feature_door_name
   FROM your_table t1
   LEFT JOIN cart c ON t1.door_id = c.door_id

Open in new window


Author Comment

ID: 41767986
When I do this:

select distinct c.door_id, d.feature_door_name from cart c INNER JOIN doors d on where c.session_id='i2rnvaoealphebajh9e0jsipb7'

I expect to get to "featurenames" based on the fact that I've got two distinct door_ids in the cart, but I only get one.

Author Comment

ID: 41767991

SELECT c.*, d.feature_door_name FROM doors d LEFT JOIN cart c ON = c.door_id and c.session_id='i2rnvaoealphebajh9e0jsipb7' me this:

too many
I'm missing something. I need to see:

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..that's it.

What have I got to do?
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LVL 52

Accepted Solution

Ryan Chong earned 250 total points
ID: 41768179
try this
SELECT c.door_id , d.feature_door_name 
FROM cart c LEFT JOIN doors d ON = c.door_id 
Where c.session_id='i2rnvaoealphebajh9e0jsipb7' 
group by c.door_id , d.feature_door_name

Open in new window

LVL 41

Assisted Solution

Sharath earned 200 total points
ID: 41768416
try other way around for LEFT JOIN.
SELECT c.* , d.feature_door_name 
FROM cart c LEFT JOIN doors d ON = c.door_id 
Where c.session_id='i2rnvaoealphebajh9e0jsipb7' 

Open in new window

LVL 29

Assisted Solution

by:Olaf Doschke
Olaf Doschke earned 50 total points
ID: 41768485
Since you start with the doors, you get all doors. Depsite of selecting all door fields as right fields in your field list, it's the "left" table the join starts from, therefore all the NULL rows for doors not having a cart entry. Simply start any query from the main table you want to query and join side data to this, not the other way around.

You might do the RIGHT JOIN instead, but I have to go far back to look where I ever needed this, it's typically only needed in conjunction with at least three tables, as you can of course always switch the order of two tables to make the join a left join. What matters is the order in which tables  are joined in the query, not the orientation of columns in the result.

Bye, Olaf.

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