Optimisation of the performance of the query using views

Question

I have created views for my project now I want to optimize them for the speed purpose. How can I identify that the view can be optimize? Is index useful for this.

SELECT DISTINCT     
        ent.ID_Entreprise, 
ct.Siret,
ct.Scont,
ct.Cont,
ct.Souscont, 
ct.Entappcr, 
ct.Cb, 
ct.Sptf,
ct.Socuti, 
ct.EntiteTPG, 
ct.Datefcb, 
ct.Dtfineffcb, 
ct.Stacb, 
ct.Libstacb, 
ct.Perap, 
ct.Libperap, 
ct.Deremis, 
ct.Derregl, 
ct.typepdt, 
ct.Libtypepdt, 
ct.Libpdt, 
ct.Libcb, 
ct.CodeICX, 
ct.AppLeader, 
(CASE ct.typepdt 
WHEN 'S' THEN '1'
WHEN 'P' THEN '2' 
WHEN 'R' THEN '3' 
WHEN 'E' THEN '3'
WHEN 'I' THEN '4' 
ELSE '5' END) AS orderParam, 
ct.Reg, 
ct.ent_opt_set, 
'' AS CdGraReg, 
'' AS CaisseSS, 
'' AS CentreSS, 
ct.affilSalEnabled, 
ct.AtOperationnel,
ct.Formule, 
ct.FormuleSocle, 
ct.Srs, 
ct.Cntcb_actif, 
ct.Libstacb_vision_C, 
ct.DATPA, 
ct.DATENVOI, 
ct.DATREGUL,
ct.UC,
ct.Art39, 
ct.Dateff, 
ct.Cnt_actif, 
ent.Raisoc, 
ct.mensualisation, 
ct.repartition, 
ct.optFin, 
ct.Date_hors_infocentre,
ent.visionC   

FROM dbo.VW_Entreprise AS ent INNER JOIN dbo.VW_Contrats AS ct ON ent.Siret = ct.Siret AND ct.Entappcr = ent.entApp

I am using two views VW_Entreprise and VW_Contrats

Answer 1

For this JOIN :

dbo.VW_Entreprise AS ent 
INNER JOIN dbo.VW_Contrats AS ct ON ent.Siret = ct.Siret AND ct.Entappcr = ent.entApp

You want the following indexes:

VW_Entreprise(Siret, entApp)
VW_Contrats(Siret, Entappcr)

If these index do not yet exist, please create them. It is hard to provide more suggestions without knowing more about your data structure and the definition of underlying views. A few hints though:

• SELECT DISTINCT implies more work for your RDBMS, since it needs to check for duplicates (and you are returning a large number of columns); make sure that you really need it before using it
• Querying views means that, under the hood, your RDBMS will somehow need to run the queries that define the views; it is sometimes more efficient to query directly the underlying tables (but once again, that cannot be told for sure without seeing the actual definition of the views)