From: Tom Hart <tomhart@coopfed.org>
To: Colin Wetherbee <cww@denterprises.org>
Cc: PG-SQL List <pgsql-sql@postgresql.org>
Subject: Re: outer join issues
Date: Wed, 06 Feb 2008 17:37:15 -0500
Message-ID: <47AA369B.70906@coopfed.org> (raw)
In-Reply-To: <47AA2E6E.7020402@denterprises.org>
References: <47AA2864.3080806@coopfed.org>
<47AA2E6E.7020402@denterprises.org>
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)
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To: pgsql-sql@postgresql.org
Cc: tomhart@coopfed.org, cww@denterprises.org
Subject: Re: outer join issues
In-Reply-To: <47AA369B.70906@coopfed.org>
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