Fix invalid Texinfo formatting and rephrase text.

@item

You can only have up to 255 @code{ENUM} and @code{SET} columns in one table.

@item

In @code{MIN()}, @code{MAX()} and other aggregate functions, MySQL

currently compares @code{ENUM} and @code{SET} columns by their string

value rather than by the string's relative position in the set.

@item

@code{safe_mysqld} redirects all messages from @code{mysqld} to the

@code{mysqld} log.  One problem with this is that if you execute

@code{MAX()} may take a string argument; in such cases they return the

minimum or maximum string value. @xref{MySQL indexes}.

There is one inconsistency in MySQL  in handling @code[ENUM] and @code[SET]

types when it comes to @code{MIN()}, @code{MAX()} and other aggregating 

functions. MySQL will compare values based on string values of the columns,

instead of it's relative position. This will be fixed in future.

@example

mysql> SELECT student_name, MIN(test_score), MAX(test_score)

    ->        FROM student

    ->        GROUP BY student_name;

@end example

In @code{MIN()}, @code{MAX()} and other aggregate functions, MySQL

currently compares @code{ENUM} and @code{SET} columns by their string

value rather than by the string's relative position in the set.

This will be rectified.

@findex SUM()

@item SUM(expr)

Returns the sum of @code{expr}.  Note that if the return set has no rows,