public static Expression dateTruncStr(Expression expression, DatePart part) {
        return x("DATE_TRUNC_STR(" + expression.toString() + ", \"" + part.toString() + "\")");
    }
public static Expression dateTruncStr ( Expression expression , DatePart part ) { return x ( "DATE_TRUNC_STR(" + expression . toString ( ) + ", \"" + part . toString ( ) + "\")" ) ; }
Returned expression results in ISO 8601 timestamp that has been truncated
so that the given date part is the least significant.