Given the following body of a case expression:

1    WHEN r.code= '00'                        then 'A1'
2    WHEN r.code ='01' AND r.source = 'PXWeb' then 'A2'   <
3    WHEN r.code ='0120'                      then 'A3'
4    WHEN r.code ='01'                        then 'A4'   <
5    WHEN r.code ='1560'                      then 'A5'
6    WHEN r.code ='1530'                      then 'A6'
7    WHEN r.code ='1550'                      then 'A7'

I'm assuming line 2 will always execute before line 4? Then I read statements like 'SQL is a declarative language, meaning that it tells the SQL engine what to do, not how' in

Order Of Execution of the SQL query

and wonder if this also relates to the order of execution in the CASE expression. Essentially, can I leave the code above as it is without having to change line 4 to

4    WHEN r.code ='01' AND r.source != 'PXWeb' then 'A4'