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Annoying join problem & frozen brain. Expand / Collapse
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Posted Tuesday, August 21, 2012 4:09 AM
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create table A
(a int, b int)

create table D
(a int)

insert into A values (1,1)
insert into A values (2,1)
insert into A values (1,2)
insert into A values (4,2)

-- this table has other values.
insert into D values (1)
insert into D values (2)
insert into D values (3)
insert into D values (4)

-- I want to join A & D based on a values where A.b = 1
SELECT * FROM D
LEFT OUTER JOIN a
ON A.a = D.a
WHERE A.b = 1
-- but have the D values 3 & 4 show up with NULL where the A values should be :
-- like this:
1 1 1
2 2 1
3 null null
4 null null

-- In reality, it's more complex based on a big IN clause that I'm trying to avoid using twice.
SELECT * FROM D
LEFT OUTER JOIN a
ON A.a = D.a
WHERE A.b = 1
AND D.a IN
(1,2,3,4)

-- Appreciate any help!
Post #1347671
Posted Tuesday, August 21, 2012 4:19 AM
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SELECT a2.a, D.a
FROM D
LEFT JOIN
(
SELECT * FROM A
WHERE A.b = 1
) AS a2
ON a2.a = D.a
WHERE D.a IN (1,2,3)

oh dear. i think the act of clarifying in a post sorted my brain out & the above code does what I need. sorry to have bothered!!

one of those days.

:)
Post #1347678
Posted Tuesday, August 21, 2012 4:23 AM


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Like this?

SELECT * FROM D
LEFT JOIN ( SELECT *
FROM
A
WHERE
A.b = 1
) AS A
ON D.a = A.B



==========================================================================================================================
A computer lets you make more mistakes faster than any invention in human history - with the possible exceptions of handguns and tequila. Mitch Ratcliffe
Post #1347680
Posted Tuesday, August 21, 2012 4:24 AM


Say Hey Kid

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Didn't see you had already sorted it!

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A computer lets you make more mistakes faster than any invention in human history - with the possible exceptions of handguns and tequila. Mitch Ratcliffe
Post #1347681
Posted Tuesday, August 21, 2012 4:27 AM


Old Hand

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You need to put the condition in the join clause:


SELECT D.a, A.a, A.b
FROM D
LEFT OUTER JOIN A
ON A.a = D.a And A.b=1
WHERE A.b = 1 or A.b is null


Post #1347682
Posted Tuesday, August 21, 2012 4:30 AM


Old Hand

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In fact you don't need the WHERE clause:


SELECT D.a, A.a, A.b
FROM D
LEFT OUTER JOIN A
ON A.a = D.a And A.b=1


...but you've fixed it. Anyway - there are a few ideas there...
Post #1347683
Posted Tuesday, August 21, 2012 4:37 AM
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Thank you both!! Appreciate you taking the time.

:)
Post #1347688
Posted Tuesday, August 21, 2012 4:41 AM


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SELECT * 
FROM D
LEFT OUTER JOIN a
ON A.a = D.a
WHERE
A.b = 1 -- << this turns the LEFT OUTER JOIN into an INNER JOIN
AND D.a IN (1,2,3,4)

-- use this instead:
SELECT *
FROM D
LEFT OUTER JOIN a
ON A.a = D.a AND A.b = 1
WHERE D.a IN (1,2,3,4)

Ah, Laurie beat me to it.


“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden
Exploring Recursive CTEs by Example Dwain Camps
Post #1347691
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