How to Optimize & Fine tune the Query?

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How to Optimize & Fine tune the Query?

Hi Friends,

I am new in Query Fine Tuning.... I know query tuning is such vast thing in DB side. We need to fine tune DB level , Business Logic , Physical Level , SQL tuning....

Can any one tel me , how to fine tune & optimize the query ? Suppose lets say if the query is taking such a long time , what are all the approach we need to take care of in our mind???

For example,

Let's say I have Query , In that i am using 7 to 8 tables , the Expected time for this query is 7mins according to the Business. But there is a case , this query is taking such a long time to give the op? I need to fine tune this???

How can i fine tune the qry ( SQL Tuning )

what are all the initial apporach i need to follow up?

how can i find out the Root Causes???

Is our Explain plan is Useful for whole tuning part ????

can any suggest me.......