SQL Server view optimization help (repeated subqueries, case when, and so on...) -

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i need optimizing mssql view is, honestly, little complex knowledge.

the view working rewrite using less subqueries or better structure in order simplify , use less server resources.

the main issue case when same subquery repeated 4 times... tried understand if can put in variable , use case instead of repeating query each time seems not possible me...

here's query

select     dbo.macchine.id_macchina, [...] dbo.view_cantieri.indirizzo,  (select     top (1) data_fine          dbo.manutenzioni      (id_macchina = dbo.macchine.id_macchina) order data_fine desc) ultima_manutenzione,   datediff(day,     (select     top (1) data_fine              dbo.manutenzioni manutenzioni_1          (id_macchina = dbo.macchine.id_macchina)     order data_fine desc), getdate()) data_diff,   (case when      stato = 0      'grey'  when stato = 2      'black'  when stato = 1              (case when              datediff(day,             (select     top (1) data_fine                      dbo.manutenzioni manutenzioni_1                  (id_macchina = dbo.macchine.id_macchina)             order data_fine desc), getdate()) >= 90          'red'          when              datediff(day,             (select     top (1) data_fine                      dbo.manutenzioni manutenzioni_1                  (id_macchina = dbo.macchine.id_macchina)             order data_fine desc), getdate()) >= 80          'orange'           when             datediff(day,             (select     top (1) data_fine                      dbo.manutenzioni manutenzioni_1                  (id_macchina = dbo.macchine.id_macchina)             order data_fine desc), getdate()) >= 60          'yellow'          when             (select     top (1) data_fine                      dbo.manutenzioni manutenzioni_1                  (id_macchina = dbo.macchine.id_macchina)             order data_fine desc) null         'red' else 'green'           end)   end)  colore         dbo.macchine inner join                   dbo.macchine_modelli on dbo.macchine.id_modello = dbo.macchine_modelli.id_modello inner join                   dbo.macchine_tipologie on dbo.macchine_modelli.id_tipologia = dbo.macchine_tipologie.id_tipologia inner join                   dbo.view_cantieri on dbo.macchine.id_cantiere = dbo.view_cantieri.id_cantiere inner join                   dbo.macchine_produttori on dbo.macchine_modelli.id_produttore = dbo.macchine_produttori.id_produttore inner join                   dbo.clienti on dbo.view_cantieri.id_cliente = dbo.clienti.id_cliente     (dbo.macchine._del = 'n')

any suggestion appreciated, if need more information db try provide it...

i notice using top(1), must 2005 or above. can keep result of datediff in outer apply subquery evaluated once.

select     m.id_macchina,     [...],     v.indirizzo,     ma.data_fine ultima_manutenzione,      ma.data_diff,      case     when stato = 0 'grey'      when stato = 2 'black'      when stato = 1         case         when ma.data_diff >= 90   'red'         when ma.data_diff >= 80   'orange'          when ma.data_diff >= 60   'yellow'         when ma.data_fine null 'red'         else 'green'          end     end colore dbo.macchine m inner join dbo.macchine_modelli on m.id_modello = i.id_modello inner join dbo.macchine_tipologie t on i.id_tipologia = t.id_tipologia inner join dbo.view_cantieri v on m.id_cantiere = v.id_cantiere inner join dbo.macchine_produttori p on i.id_produttore = p.id_produttore inner join dbo.clienti c on v.id_cliente = c.id_cliente outer apply (select top (1)                 ma.data_fine,                 datediff(day, ma.data_fine, getdate()) data_diff                dbo.manutenzioni ma               ma.id_macchina = m.id_macchina             order ma.data_fine desc) ma m._del = 'n'

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