how to select max of mixed string/int column?

Question

Lets say that I have a table which contains a column for invoice number, the data type is VARCHAR with mixed string/int values like:

invoice_number
*********         


        

Answer 1

Your problem is more one of definition & design.

Select the invoice number with highest ID or DATE, or -- if those really don't correlate with "highest invoice number" -- define an additional column, which does correlate with invoice-number and is simple enough for the poor database to understand.

select INVOICE_NUMBER 
from INVOICE_HEADER
order by ID desc limit 1;

It's not that the database isn't smart enough.. it's that you're asking it the wrong question.