Your code is correct, there are two possibilities:

• You changed the value of total before or after the code you shown. As you used raise, the transactions are rollbacked and, when you perform your manual query in SQL, you do not see the changed value. Do a cr.commit() just before raise, you may get NULL in your manual SQL query after calling the python code.
• Both tests are not on the same database.

For me works this way:

1. sql = "..."
   

2. result = self.env.cr.execute(sql)

3. value = ''

4. for res in self.env.cr.dictfetchall():

5.        if (value != ''):

6.             value += ','

7.         value += res['number']

8. 
   

9. record.invoices = value

Hope it helps

cr.execute('''SELECT code, total FROM hr_payslip_line WHERE slip_id=%s''' % (slip.id)) x = cr.fetchone() #Only if it returns one (1) row

raise osv.except_osv('Info', 'code : %s\nTotal : %s' % (x[0], x[1]))

#or to return just one row SELECT code, SUM(total) FROM hr_payslip_line WHERE slip_id=1 GROUP BY code

I guess that the problem is an interference between the function compute_sheet in the hr_payroll module and my function

I have a stored fucntion field that get total from what shown above, but I put store=False it works well, for me it's not logic and I declared this as a bug,

There is somthing that not good in this module, as a advanced developper I get always values of stored function in the database using SQL and anawhere, this time it's different for me, If I Try to use cr.commit(), there isn't any changes, if I use cr.rollback() I get an other message that say that a field quantity from the object hr_payslip_line doesn't exist, for my module there is not any treatement of field quantity

So if you have a logic to resolve this problem, I'm gratfull for you

To recap : I want to compute a stored function field, I execute the code above and it don't work