Re: (OT) perl, memory and mysql

In the spirit of give a man a fish...

SELECT        AM.AM_A, AM.AM_M

FROM        AM
LEFT JOIN    AR ON AR.AR_A=AM.AM_A
LEFT JOIN    SA ON SA.SA_A=AM.AM_A
LEFT JOIN    MR ON MR.MR_M=AM.AM_M
LEFT JOIN    SM ON SM.SM_M=AM.AM_M
#LEFT JOIN    SR ON SR.SR_M=AM.AM_M

WHERE        AR.AR_A IS NULL
AND        SA.SA_A IS NULL
AND        MR.MR_M IS NULL
AND        SM.SM_M IS NULL
#AND        SR.SR_M IS NULL
[download]

Something close to this may be closer to the result you want. I didn't see you use a WHERE clause vs the SR table, so I left it commented out.

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Re^2: (OT) perl, memory and mysql by Anonymous Monk on Feb 12, 2006 at 14:20 UTC
Hi, thanks for the response. Will using left joins and 'NULL' values give me the same response that my original query did (in the event of unlimited memory!) ? I don't really understand the use of NULL in this instance because I have no NULL values in my database and was originally checking for where two values weren't equal. Thanks again!	[reply]
Re^2: (OT) perl, memory and mysql by Anonymous Monk on Feb 12, 2006 at 15:04 UTC
Hi again, I am still trying to get to grips with left joins. How would it work for the following query? `select * from AM, AR, SA, SM, MR, SR where AR.AR_A=AM.AM_A and AR.AR_A +=SA.SA_A and SR.SR_R=MR.MR_R and SR.SR_R=AR.AR_R and AM.AM_M=MR.MR_M +and AM.AM_M=SM.SM_M and SM.SM_S=SA.SA_S and SM.SM_M=SR.SR_S;` [download] Kind regards!	[reply] [d/l]