indexing - Do mysql update queries benefit from an index? -

-

i have table updates , i'm wondering if update queries benefit having index on column , updated column or index on column?

just on column. index on update column slow down query because index has updated along data. index on column speed updates, , selects, slow down insertions.

indices cause overhead when delete rows. in general thing though on columns using where on lot, , necessary on columns joins on, or order by


Comments

Post a Comment

Popular posts from this blog

javascript - Iterate over array and calculate average values of array-parts -

-
i have array this: ["2011-06-16 16:37:20",23.2], ["2011-06-21 16:37:20",35.6], ["2011-06-26 16:37:20",41.8], ["2011-07-01 16:37:20",25], ["2011-07-06 16:37:20",22.8], ["2011-07-11 16:37:20",36.4], ["2011-07-16 16:37:20",34], ["2011-07-21 16:37:20",20] [...] format: [$date,count] now need add 3rd 4th value every array element, average of n counts before or after. example if n=3 the 3rd value should average of 3 count-values before , 4th value should average of 3 count-values after current array element. result that: ["2011-06-16 16:37:20",23.2, null, 34.13], ["2011-06-21 16:37:20",35.6, null, 29.86], ["2011-06-26 16:37:20",41.8, null, 28.06], ["2011-07-01 16:37:20",25, 33.53, 31.06], ["2011-07-06 16:37:20",22.8, 34.13, 30.13], ["2011-07-11 16:37:20",36.4, 29.86, null], ["2011-07-16 16:37:20",34, 28.06, null], ["2...
Read more

iphone - Using nested NSDictionary with Picker -

-
newbie here, i have single component picker set plist, each item being array, multiple strings in each array app uses. currently plist structure this: nsdictionary -> nsarray -> nsstring | | items in picker data each item but now, want: nsdictionary -> nsdictionary -> nsarray -> nsstring | | | different picker data sets items in picker data each item so there multiple sets of picker components show using segmented control etc... i'm not sure if possible, , hoping save me making many different separate picker controllers. what has me stumped getting ingested properly this have now, builds crashes (debug info below): nsbundle *bundle = [nsbundle mainbundle]; nsstring *plistpath = [bundle pathforresource:@"camerasdatabase" oftype:@"plist"]; nsdictionary *dictionary = [[nsdictionary alloc] initwithcontentsoffi...
Read more

objective c - Newbie question -multiple parameters -

-
i trying implement private method takes nsmutabledictionary , player object parameters. private method, place exists in ".m" file. it declared as -(void) incrementscore: (nsmutabledictionary*) scoreboard forplayer: ( player* ) player { and call follows : [ self incrementscore:deucescore forplayer:p]; however,it won't compile - may not response message -incrementscore:forplayer i'm not sure error lies - need declare method in ".h" file, or elsewhere in ".m" file, or have got syntax wrong? the compiler needs find declaration method somewhere before use it. done in 3 way: declare method in (public) @interface class in .h file . declare method in class extension (a semi-private @interface , @ top of .m files). define method somewhere in @implementation before first use of it.
Read more