[SQL] Selecting item from table, whether or not it has corresponding entry in 2nd table...

[Augustus]

Hiya!

I have a question:

I have 2 tables... "Inventory" and "Price"

These tables are used by 2 restaurants... the inventory has what they sell,
and prices has the corresponding prices to those items for each location.

What I want to do:
I want to get a list of all items in the "Inventory" table and the
corresponding price from the "Price" table for a location, unless the column
"SHOW" (in the "Price" table) is set to "N"

It might sound like "Just use a LEFT JOIN"... but if there is no entry for
the item in the "Price" table, I still want a result

I tried using:
===============
select i.name, p.price1
from inventory i
LEFT JOIN prices p
ON p.itemID=i.itemID
where (
(i.itemType=7)
AND (i.canusa='usa')
AND (p.storeID=99)
AND (p.show='y')
)

===============

But that only returns the items that have prices set up in the prices
table...

So I tried adding
===============
OR (NOT EXISTS (SELECT * FROM prices where (p.itemID=i.itemID) AND
(i.itemType=7))
)
===============

to the end of the WHERE conditions, but this returns everything in the
inventory table

I then tried changing the whole statement to:

===============
select i.name, p.price1
from inventory i
LEFT JOIN prices p
ON p.itemID=i.itemID
where (
(i.itemType=7)
AND (i.canusa='usa')
AND (p.storeID=99)
AND (p.show='y')
)
OR (i.itemType=7)
AND (i.canusa='usa')
AND (NOT EXISTS (SELECT * FROM prices where (p.itemID=i.itemID) AND
(i.itemType=7)))
===============

Now that does work... BUT, I am repeating some of the conditions of the
WHERE statement: (i.itemType=7) AND (i.canusa='usa')
And I am wondering if this is the most efficient way of doing it, or if its
just some bandaid approach that works and the true logic has escaped me?
(and is the "not exists" condition going to give some extra load the server
or not)

Any help is appreciated

Thanks,

Clint

 

[Chris Hohmann]

Hiya!

I have a question:

I have 2 tables... "Inventory" and "Price"

These tables are used by 2 restaurants... the inventory has what they sell,
and prices has the corresponding prices to those items for each location.

What I want to do:
I want to get a list of all items in the "Inventory" table and the
corresponding price from the "Price" table for a location, unless the column
"SHOW" (in the "Price" table) is set to "N"

It might sound like "Just use a LEFT JOIN"... but if there is no entry for
the item in the "Price" table, I still want a result

I tried using:
===============
select i.name, p.price1
from inventory i
LEFT JOIN prices p
ON p.itemID=i.itemID
where (
(i.itemType=7)
AND (i.canusa='usa')
AND (p.storeID=99)
AND (p.show='y')
)

===============

But that only returns the items that have prices set up in the prices
table...

So I tried adding
===============
OR (NOT EXISTS (SELECT * FROM prices where (p.itemID=i.itemID) AND
(i.itemType=7))
)
===============

to the end of the WHERE conditions, but this returns everything in the
inventory table

I then tried changing the whole statement to:

===============
select i.name, p.price1
from inventory i
LEFT JOIN prices p
ON p.itemID=i.itemID
where (
(i.itemType=7)
AND (i.canusa='usa')
AND (p.storeID=99)
AND (p.show='y')
)
OR (i.itemType=7)
AND (i.canusa='usa')
AND (NOT EXISTS (SELECT * FROM prices where (p.itemID=i.itemID) AND
(i.itemType=7)))
===============

Now that does work... BUT, I am repeating some of the conditions of the
WHERE statement: (i.itemType=7) AND (i.canusa='usa')
And I am wondering if this is the most efficient way of doing it, or if its
just some bandaid approach that works and the true logic has escaped me?
(and is the "not exists" condition going to give some extra load the server
or not)

Any help is appreciated

Thanks,

Clint

Answered in m.p.i.asp.db. Please don't multi-post:
http://aspfaq.com/5003

 

[Augustus]

Answered in m.p.i.asp.db. Please don't multi-post:
http://aspfaq.com/5003

Thanks Chris

I originally meant to crosspost to the 2 groups... it fit in the other one
better than this one, but this one sees alot more activity and has answered
most of my SQL questions pretty quickly...

Clint

 

[Ken Fine]

Clint:

Be advised that people here hate it when you crosspost, even in
meaningful/relevant groups. It burns folks up to spend a lot of time
answering a question that's already been answered elsewhere.

We've all done it, so it isn't a capital crime, but it's probably best to
observe people's sensitivities in this matter.

-KF