[Qgis-user] Coding in the field calculator - how to ask for value one line above

[Florian Konrad]

Hi there,
i got an attribute-table with thousands of lines and several columns. I want to check every Line if the value in column „X" is „a“ and if the value in column „Y“ but one line above is „b“ at the same time. So i want to write something like this in the field calculator to generate a new column:

CASE WHEN „X" = ‚a' AND "the value one row above in column Y" = ‚b' THEN '1‘ END

so that i can mark these lines that im searching for with ‚1‘ in a new column… Is there a command for "the value one row above in coloum Y“ ? Or do i have to do this some other way?
I hope i explained my problem well enough and would appreciate any help.

Greetings 
Florian