MySQL Server supports three comment styles:
From a "
#" character to the end of the line.
From a "
-- " sequence to the end of the line. In MySQL, the "
-- " (double-dash)
comment style requires the second dash to be followed by at least one whitespace or control character
(such as a space, tab, newline, and so on). This syntax differs slightly from standard SQL comment
syntax, as discussed in Section 184.108.40.206, "'
--' as the Start of a Comment".
/* sequence to the following
*/ sequence, as in the C programming language. This syntax enables a comment
to extend over multiple lines because the beginning and closing sequences need not be on the same line.
The following example demonstrates all three comment styles:
SELECT 1+1; # This comment continues to the end of linemysql>
SELECT 1+1; -- This comment continues to the end of linemysql>
SELECT 1 /* this is an in-line comment */ + 1;mysql>
this is a
Nested comments are not supported. (Under some conditions, nested comments might be permitted, but usually are not, and users should avoid them.)
MySQL Server supports some variants of C-style comments. These enable you to write code that includes MySQL extensions, but is still portable, by using comments of the following form:
In this case, MySQL Server parses and executes the code within the comment as it would any other SQL statement,
but other SQL servers will ignore the extensions. For example, MySQL Server recognizes the
STRAIGHT_JOIN keyword in the following statement, but other servers will not:
SELECT /*! STRAIGHT_JOIN */ col1 FROM table1,table2 WHERE ...
If you add a version number after the "
!" character, the syntax within the comment is executed only if the
MySQL version is greater than or equal to the specified version number. The
TEMPORARY keyword in the following comment is executed only by servers from MySQL
3.23.02 or higher:
CREATE /*!32302 TEMPORARY */ TABLE t (a INT);
The comment syntax just described applies to how the mysqld server parses SQL statements. The mysql client program also performs some parsing of statements before sending them to the server. (It does this to determine statement boundaries within a multiple-statement input line.)
Comments in this format,
/*!12345 ... */, are not stored on the server. If this
format is used to comment stored routines, the comments will not be retained on the server.
The use of short-form mysql commands such as
/* ... */ comments is not supported.