Question

My current query works just fine outside of the CASE WHEN:

select *, timestampdiff(DAY, from_unixtime(laststaffreplytime, '%Y-%m-%d'), 
curdate()) from swtickets;

However, when this is placed in the ELSE of a CASE WHEN, the column produces all null values:

SELECT *, CASE laststaffreplytime
WHEN 0 THEN 'No Response' 
ELSE (timestampdiff(DAY, from_unixtime(laststaffreplytime, '%Y-%m-%d'), 
curdate())) END as LastContact from swtickets;

Any ideas as to why this query is returning only null values?

Answer 1

The CASE operator has to be able to return a single data type — your sample returns a string in one case, and an integer in the other. I don’t think that should turn the results into NULLs — I would expect that the integers would be represented as strings in that case — but anything’s possible with MySQL 🙂

Try changing the “No Response” to a fixed integer value, like -1, to see if that changes the results.

From the manual:

The return type of a CASE expression is the compatible aggregated type of all return values, but also depends on the context in which it is used. If used in a string context, the result is returned as a string. If used in a numeric context, the result is returned as a decimal, real, or integer value.