Top 1 faster if only selecting one row

Does the database break the selection loop as fast as it has got one record when using Top 1?

So that select top 1 * from customer where cusId = 1234

is faster than select * from customer where cusId = 1234 ?

cusId is unique, so does MSSql understand to do it "faster" without top 1 ?

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If cusId is a primary key, both should be the same re: performance.

EDIT:

You are only adding overhead with TOP 1 if you have unique index that will return 1 result anyway.

It will be different if you have order by something than you are interested in only one row.

MORE:

There is no looping involved, unless there is a table scan involved and there is no index at all for cusId . In that case, TOP 1 can't help you anyway.

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在我看来， select * from customer where cusId = 1234会更快..它有一个操作比第一个操作更少...

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