How to understand what is written here?

Question

Transact SQL

Help me figure out the SQL query, I can’t understand why quadrant brackets are needed, i.e. why are they even needed in the example and T-SQL in general?

SELECT TOP (10) [M].[membershipId]
FROM Membership AS [m]

Answer 1

The parentheses are required if you use keywords or special characters in column names or identifiers. You can name the column [First Name] (with a space) - but then you will need to use parentheses every time you refer to that column. Otherwise, square brackets are optional.
For example, your request could be written like this:

SELECT TOP (10) m.membershipId FROM Membership AS m;

but

SELECT TOP (10) m.[Member Name] FROM [Service Membership] AS m;

MS SQL fiddle