Diff between Top 1 1 and Select 1 in SQL Select Query

Question

I have a general doubt in sql. What is actually "Top 1 1" will do ? What is the meaning of the below query ?

select top 1 1 from Worker W where not exists (select 1 from Manager M where M.Id = W.Id)

what is the diff between select "TOP 1 1" and "SELECT 1" in sql server query ?

Answer 1

SELECT TOP 1 Means Selecting the very 1st record in the result set

SELECT 1 Means return 1 as the result set

SELECT TOP 1 1 FROM [SomeTable] WHERE <SomeCondition> Means if the condition is true and any rows are returned from the select, only return top 1 row and only return integer 1 for the row (no data just the integer 1 is returned).

Answer 2

In the following, the first "1", which is part of the "TOP 1" means to stop after it gets to a single result. The second "1" is just because the author really does not care what the result is.

SELECT TOP 1 1 FROM WORKER

is essentially the same as

SELECT TOP 1 * FROM WORKER

The only question is whether it would be more efficient in the "EXISTS" part of the query than just

SELECT 1 FROM Manager...

Answer 3

The request finds if there is at least one worker (top 1) with no manager. The SELECT 1 clause acts as a "return true".

If there is a manager, the request select 1 from Manager M where M.Id = W.Id returns 1. If there is no manager, the request returns NULL.