kimberly_lehman (6/6/2014)
Number 2 is selecting names of employees over 60. Or specifically, people who were 60 years old by the end of last year, since this is only comparing by year. I have no idea which ones provides better performance. In my experience I either haven't worked with large enough data sets that I needed to spend time optimizing queries, or the companies I worked for were large enough that DBAs would handle the optimizing of queries that took too long to run.
The second one is better for performance. In the first one, an index on DateOfBirth cannot be used, as the column is inside a calculation.
The second one doesn't have this problem.
Regarding the remark of Luis saying the results can be different:
I think this is becausue DATEDIFF(year,date1,date2) isn't exactly accurate. 20131231 and 20140101 gives a 1 year difference, but in reality they are just 1 day apart.
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