[] brackets in sql statements

Question

What do the brackets do in a sql statement?

For example, in the statement:

insert into table1 ([columnname1], columnname2) values (val1, val2)

Answer 1

They are meant to escape reserved keywords or invalid column identifiers.

CREATE TABLE test
(
  [select] varchar(15)
)

INSERT INTO test VALUES('abc')

SELECT [select] FROM test