SQL rtrim选择和分组

Question

If you put an rtrim in the SELECT and also again in the GROUP BY, is this inefficient because its rtriming twice, one in the select and one in the group by? eg...

SELECT
rtrim(people.FORENAME1)+ ' ' + rtrim(people.SURNAME)AS Full_Name,

FROM 
my table

GROUP BY 
rtrim(people.FORENAME1)+ ' ' + rtrim(people.SURNAME)

Answer 1

It's probably only performing the function once, but it's inefficient since it's non SARGable.

Since you are applying a function, the optimizer can't use any existing indexes that refer to those fields. It doesn't know the results of the function(s) until they are run, so it needs to process each and every row in the table.