presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitColumnDefinition
class AstBuilder:    @Override
    public Node visitColumnDefinition(SqlBaseParser.ColumnDefinitionContext context)
    {
        Optional<String> comment = Optional.empty();
        if (context.COMMENT() != null) {
            comment = Optional.of(((StringLiteral) visit(context.string())).getValue());
        }

        List<Property> properties = ImmutableList.of();
        if (context.properties() != null) {
            properties = visit(context.properties().property(), Property.class);
        }

        boolean nullable = context.NOT() == null;

        return new ColumnDefinition(
                getLocation(context),
                (Identifier) visit(context.identifier()),
                (DataType) visit(context.type()),
                nullable,
                properties,
                comment);
    }