1. NULLs and Other SQL Gotchas
Wendy Pastrick

2. About DBA since 2000 Salesforce Performance DBA
Data Platform MVP since 2013
PASS Board of Directors – Educational Content

3. Data Data Data Null ANSI settings Unknown NULL = NULL
Validation
ISNULL
= NULL

4. No Data? Empty vs Null Datatype matters! Integer String Date
converts to 0
String
Empty (‘’)
Date
:00:00.000

5. Fallout
Your SQL code that would otherwise expect to work like the IS NULL or IS NOT NULL checks won’t work anymore
In case you were doing this for a number column, the aggregate functions like AVG() which otherwise would be ignoring the Null value will now count the record

6. Fallout…more
The SQL code which uses functions like ISNULL(), COALESCE() etc. will not function as expected since these fields will not have a Null value.
The sorts won’t work as expected since Null and the empty string (and the subsequent default value that actually gets inserted) are not the same thing.

7. ….and even More
If you have this column as part of the foreign key, you will get an error at the time of the insert itself since instead of a Null value, the code will try to insert another default value in and it will violate the FK constraint.
Any concatenation operations or MAX(), MIN() functions can lead to un-desired results.

8. Scalar Functions Performance killer RBAR
Only returns a single value per input
Table Valued Functions preferable, but still not awesome.

9. Date and Time
Discussion

10. Thank You! Wendy.Pastrick@gmail.com Resources
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