(mysql.info) comments

 
 9.4 Comment Syntax
 ==================
 
 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 
      ansi-diff-comments.
 
    * From a `/*' sequence to the following `*/' sequence, as in the C
      programming language. This syntax allows 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:
 
      mysql> SELECT 1+1;     # This comment continues to the end of line
      mysql> SELECT 1+1;     -- This comment continues to the end of line
      mysql> SELECT 1 /* this is an in-line comment */ + 1;
      mysql> SELECT 1+
      /*
      this is a
      multiple-line comment
      */
      1;
 
 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:
 
      /*! MYSQL-SPECIFIC CODE */
 
 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.)
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