$sql =~ s{
(create\s+table\s+\w+\s*\()         # "create table foo (", save as $1
   (                                # Save all the elements as $2
      (                             # Grab this pattern (each of the create table variables), save as $3
            \s*                     # Any spaces
            \w+                     # Variable name
            \s+                     # At least one space
            \w+                     # Variable type
            (                       # Optional (nnn) for character string types, save as $4
               \(                   # Literal open paren
               \d+                  # Any number of digits
               \)                   # Literal close paren
            )?                      # The ? makes it optional
            \s*                     # Any spaces
            [\w\s]*                 # Any words and/or spaces ("null" or "not null", specifically)
            ,?                      # Optional comma (optional as it may be the last element)
            \s*                     # Any spaces
      )+                            # Match this whole section at least once
   )
(\s*\)\s*)                          # Closing paren for create table block with surrounding whitespace, save as $5
}
{
	@elements = split(/,/, $2);
	foreach $elem (@elements) {
		if ($elem =~ /null\s*$/i) { next; }
		$elem .= " NOT NULL";
	}
	$1 . (join ",", @elements) . $5	
}gex;