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To improve the query performance we need to follow the below check list.
1. run the query & check the execution plan
2. in the execution plan if we are seeing table scan it means there is not index created. we need to create index on that table ( the column which selected in select list)
3. if there is index is created but still ur getting table scan then need to check on which column the index has been created.. we need to make sure index has been created on the column which has int value .. coz the performance will hit if u have created index on Name column
4. from the execution plan we need to find how many hints we are getting based on that we need to modify the query.. hints are nothing but the suggestion for better performance.
5. there should not more index created on same table. else that will become problem.
6. what is the network speed .. that also matter for the performance issue.

By using Indexes, i.e., creating clustered, and non-clustered indexes, whenever its required.

is it related to DB querry?

adding indexes is not the only way of improving query performance .. it can be improved by rewriting queries as well .. Rewrite to reduce joins ,, move projections on top will help too.