Comments indicate user-provided text. There are two different types of comments: the — comment and the /*…*/ comment. Comments can be inserted on a separate line, nested (– only) at the end of a SQL command line, or within a SQL statement. The comment is not evaluated by the server. Two hyphens (–) is the SQL-92 standard indicator for comments.
FROM table1 — this is a comment
INNER JOIN table2 ON table1.c1 = table2.c1
/* this is another comment */
WHERE table1.c1 > 10
ORDER BY table1.c1