Message-ID: <47AA369B.70906@coopfed.org>
Date: Wed, 06 Feb 2008 17:37:15 -0500
From: Tom Hart <tomhart@coopfed.org>
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To: Colin Wetherbee <cww@denterprises.org>
CC: PG-SQL List <pgsql-sql@postgresql.org>
Subject: Re: outer join issues
References: <47AA2864.3080806@coopfed.org> <47AA2E6E.7020402@denterprises.org>
In-Reply-To: <47AA2E6E.7020402@denterprises.org>
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Colin Wetherbee wrote:
> Tom Hart wrote:
>> Let me preface this by saying hello SQL list, and I'm an idiot. My 
>> SQL knowledge is advanced to the point of being able to use a WHERE 
>> clause basically, so I appreciate your business. Now on to my issue
>>
>> I have 3 tables I'm trying to use in this query: loan, share and 
>> draft (for those of you not familiar with credit unions, share and 
>> draft are savings and checking accounts). What I'm trying to do is 
>> get a list of all loans that were charged off (ln_chgoff_dt > 0), and 
>> any share and draft accounts that have the same account number. My 
>> query looks something like this
>>
>> SELECT ln_acct_num, ln_num, ln_chrgoff_dt, ln_chrgoff_amt, 
>> sh_balance, sh_stat_cd, df_balance, df_stat_cd
>> FROM loan
>> LEFT OUTER JOIN share ON loan.ln_acct_num = share.sh_acct_num
>> LEFT OUTER JOIN draft ON loan.ln_acct_num = draft.df_acct_num
>> WHERE
>>  ln_chrgoff_dt > 0
>>  AND loan.dataset = 0
>>  AND share.dataset = 0
>>  AND draft.dataset = 0
>> ;
>>
>> Now the query
>> SELECT * FROM loan WHERE ln_chrgoff_dt > 0 AND loan.dataset = 0
>> returns 139 rows. Shouldn't the first query return at least that 
>> many? My understanding is that a LEFT OUTER JOIN will not drop any 
>> records that are only found in the first table, regardless of whether 
>> they match records on the second or third table. I end up with 14 
>> results with the first query. I know I'm doing something wrong, but 
>> I'm not sure what. Anybody have a helpful kick in the right direction 
>> for me?
>
> My "I looked at this for 20 seconds" guess is that the following 
> clauses are messing you up.
>
> >  AND share.dataset = 0
> >  AND draft.dataset = 0
>
> The LEFT OUTER JOIN isn't helping you if you're still comparing values 
> in the JOINed tables in the WHERE clause.
>
> Colin
Thank you for the responses everybody. I actually had somebody in the 
irc channel help me figure this one out. For the record here's my 
complete query (there's more additions, like a couple CASE's to 
translate numbers to strings)

SELECT
    ln_acct_num,
    ln_num,
    ln_chrgoff_dt,
    ln_chrgoff_amt,
    sh_balance,
    CASE WHEN sh_stat_cd = 0 THEN 'Open' ELSE 'Closed' END as sh_stat_cd,
    COALESCE(df_balance::text, 'No Draft'),
    CASE WHEN df_stat_cd = 0 THEN 'Open' ELSE 'Closed' END as df_stat_cd
FROM loan
LEFT OUTER JOIN (select * from share where dataset = 0) as share ON 
loan.ln_acct_num = share.sh_acct_num
LEFT OUTER JOIN (select * from draft where dataset = 0) as draft ON 
loan.ln_acct_num = draft.df_acct_num
WHERE
  ln_chrgoff_dt > 0
  AND loan.dataset = 0
  AND sh_balance IS NOT NULL
;

-- 
Tom Hart
IT Specialist
Cooperative Federal
723 Westcott St.
Syracuse, NY 13210
(315) 471-1116 ext. 202
(315) 476-0567 (fax)