Comments

A comment is a note for people; the database skips it. In SQL, a comment starts with two dashes, --, and goes on to the end of the line:

-- Games for the summer sale
SELECT title, price
FROM games; -- the price is in dollars

A longer note can span several lines between /* and */:

/* The shop's newsletter goes to every customer.
   It needs their names and emails. */
SELECT name, email
FROM customers;

Comments explain what a query is for, which isn't always clear from the query itself. They are also handy when you want a statement to stop running for a while, without deleting it: put -- in front of it. Programmers call that commenting out. To make the statement run again, delete the dashes.

A statement that spans several lines needs -- in front of each of its lines, or you put it all between /* and */.