Better ask your friend to prove his point.

AFAIK using an alias has no performance impact and
in the execution plan, the cost for the query with and without the
alias are same.

Using Alias is a good programming practice because it improves the
readability of the code, and in case of table variables you cannot avoid
them.

--
Roji. P. Thomas
SQL Server Programmer
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friend told that alias name will decrease the performance of the query. Is
it right? I have used aliasing in so many queries.
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