Comments

Single-line comments

Single line comments are preceded by --, and go until the end of the line:

SELECT *
FROM Employees -- this is a comment
WHERE FName = 'John'

Multi-line comments

Multi-line code comments are wrapped in /* ... */:

/* This query
   returns all employees */
SELECT *
FROM Employees

It is also possible to insert such a comment into the middle of a line:

SELECT /* all columns: */ *
FROM Employees