Store the result of a select query into an array variable

Consider the following SELECT query:

SELECT CourseID FROM Course

with data:

CourseID
112
101
125
173
145
152
160

We try to store the above result set into a variable. We try it like this:

DECLARE @a VARCHAR(MAX)
SELECT @a=CourseID FROM Course

Giving a PRINT @a returns just the last value: 160. So, obviously, we cannot store 7 discrete values inside a scalar variable. We can use a table variable instead:

DECLARE @a TABLE (id int)
INSERT INTO @a
SELECT CourseID FROM Course

As you might have guessed giving a PRINT @a this time returns a syntax error. The correct way to access @a is to treat it like an ordinary table:

SELECT id FROM @a