Hi Dan, <Sending this to general list too since it's not a Windows specific question.>
Just run the UPDATE with all the column you want to update. :-) MySQL won't update the ones that haven't changed (which may have been said). Don't waste time trying to determine whether you should include a column in the UPDATE or not. The only time it could be an issue is if you're setting a column to a *REALLY* long value. It will take longer to send the query to the server (especially over a network) and MySQL will take a little more time to parse it. Hope that helps. Matt ----- Original Message ----- From: "Daniel Canham" Sent: Monday, January 12, 2004 2:48 AM Subject: Re: query efficiency > Thats not really what I meant. I have 5 (or whatever) columns in a table. > I need to update values changed in those columns during processing. But I > have no way of knowing what column values need updating. Is it worth my > while to write a dirty field checker (value has changed) or doesn't the > mysql engine care on UPDATE whether it is UPDATEing 1 or all 10 columns. > The way you have it, you are doing all UPDATEs in one statement, or each > column on a seperate UPDATE. In that case obviously it is faster to run one > update. My question was is it more efficient to execute an single statement > UPDATE that has just the changed columns, or a single statement UPDATE that > contains all columns every time because the mysql engine treats them the > same. > > -Dan > > > > > -----Original Message----- > From: robert_rowe [mailto:[EMAIL PROTECTED] > Sent: Saturday, January 10, 2004 1:17 PM > To: [EMAIL PROTECTED] > Subject: [mysql] Re: query efficiency > > > > By the way, MySQL won't actually do the update is the existing value is the > same as what is already in the fields. Try something like this: > > <pseudocode> > print now > > for i=1 to 10000 > update table1 set col1=i+4, col2=i+3,col3=i+2,col4=i+1,col5=i; > next i > > print now > > for i=1 to 10000 > update table1 set col1=i+4 > update table1 set col2=i+3 > update table1 set col3=i+2 > update table1 set col4=i+1 > update table1 set col5=i > next i > > </pseudocode> > > I suspect that the first way will be faster. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
