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From:Colin McKinnon Date:April 14 1999 2:25pm
Subject:Re: balances
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At 20:05 14/04/99 +1000, Michael Farr wrote:
>I would like to query a table with two columns, 1st being just a key field,
>second being a debit field (float) ie
>service	|	debit
>1		|	50
>2		|	100
>3		|	-30
>I would like to query the table with a select and get back a balance field
>calculated at run time as well ie
>select debit, balance()
>from account
>debit		|	debit
>50		|	50
>100		|	150
>-30		|	120
>Is this possible in MySQL?  I read that I may be able to say create
>function balance() to create that function, but I don't know how to do that!
>Any ideas would be muchly appreciated.

AIR It's just possible to do in *some* SQL dialects but it is an
EXCEEDINGLY difficult thing to do - the DBMS must have some sense of
sequence, which technically speaking, one based on a relational calculus
does not. In other words - I don't think it's feasible with MySQL which is
a very minimalist system (which is why I like it). Although it may be
possible to acheive on other systems, I don't think it's advisable.

Having said that, there's nothing to stop you accessing the data in a
different language and generating the figures for yourself, or developing a
tool to automatically maintain the data in the other column. I suppose you
could even write a MySQL function which retains some state from one row to
the next although you may then encounter some unexpected problems.


balancesMichael Farr14 Apr
  • Re: balancesColin McKinnon14 Apr
  • Re: balancesChristian Mack14 Apr
  • balancesMichael Widenius15 Apr