Finding/searching for missing values in MySQL

Question

I am using MySQL and have a table called sales. Its primary key is sales_id.

-------------------------------------
sales_id | invo         


        

Answer 1

You can find gaps in a MySQL sequence using this query:

SELECT invoice_id+1
   FROM sales s
   WHERE NOT EXISTS (
       SELECT NULL
       FROM sales t
       WHERE s.invoice_id = t.invoice_id+1
   ) 
   HAVING `invoice_id+1` < (SELECT MAX(invoice_id) FROM sales)
   ORDER BY invoice_id

This will return all invoice_id missing from the sequence, regardless of sales_id.