# Errors considered harmful **URL:** \ **Category:** Request For Comments\ **Created:** [February 8, 2021, 5:54pm UTC](https://swi-prolog.discourse.group/t/errors-considered-harmful/3574 "2021-02-08T17:54:43Z")\ **Posts on this page:** 1\ **Showing post:** 102
**Author:** ![peter.ludemann](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/peter.ludemann/32/48_2.png) [@peter.ludemann](https://swi-prolog.discourse.group/u/peter.ludemann)\ **Post date:** [February 16, 2021, 12:30am UTC](https://swi-prolog.discourse.group/t/errors-considered-harmful/3574/102 "2021-02-16T00:30:57Z")
> [@anon95304481](#): > > Interestingly SQL has a better standing here. Since a) it has null values > and b) these are handled via [3-valued logic in SQL](https://modern-sql.com/de/konzept/dreiwertige-logik). SQL also gets it wrong with NULLs. Consider a table with these values: ```prolog A B 0 1 1 null ``` then sum(A) + sum(B) = 2 but sum(A+B) = 1. (And I have more examples of other problems with SQL’s null.) For those who want to try this out (I used sqlite): ```prolog create table t(a int, b int); insert into t(a,b) values(0,1); insert into t(a,b) values(1,null); select sum(a)+sum(b), sum(a+b) from t; ``` --- _[View the full topic](https://swi-prolog.discourse.group/t/errors-considered-harmful/3574)._