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Posted by Jonas Smith on 10/06/97 11:59
I'm trying to understand triggers before trying my hand at implementing
one. I tried reading the documentation on mysql's site, but it's not
detailed enough.
I have a large table. There is a calculation currently done on the
client side that I would like to put on the server side.
The calculation needs to happen on updates.
the table has many columns but to simplify:
table
idColumn
articleTitleColumn
totalColumn
votesColumn
canceledColumn
scoreColumn
accessColumn
Whenever a member accesses the news article, the 'accessColumn' is
incremented by one.
When a member rates the article, the totalColumn is incremented by the
amount of the score and the votesColumn is incremented by one.
Under certain conditions some votes are cancelled; in those cases the
cancelled column is incremented.
The calculation is:
scoreColumn = totalColumn / (votesColumn - canceledColumn)
The first question is:
Can the trigger be set to do the calculation only when the totalColumn
is updated? The access column is updated quite often (as well as other
columns) and to trigger the calculation any time any of the columns is
updated would put undue load on the servers.
Second question:
What is the syntax for this kind of trigger?
thanks in advance for any pointers.
--
Jonas
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