cost of an SQL Query

[anuanil]

Hi,

I need an answer in SQL. Can anyone please explain me what is meant by Cost of an SQL Query? Where does we use this and what is the use of this technology?

[corihuela]

I don't think that we're taking about a technology.

And the direct answer I could give you I that The cost of an SQL Query is the amount of time and resources that X query will use at a given machine. I.E. The cost of executing a simple query like:

select * from a_table;

Would depend on the size of that table. Could be from .000000000001 seconds to say, 3 or 4 minutes. And The query could block the access to the database in the meanwhile.

As a rule of thumb try to restrict your queries as much as you can.

select <specific_fields> from <table> where <max_restrictions>

[blazingrock4u]

How do I calculate the (full) Cost of a query?

[rajinikanthm]

1) select cost (choose) based optimisation.
2) Analyse the corresponding tables.(user alter statements)
3) Generate explain plan for the sql (set autotrace or explain plan for the statement)
4) Analyse with the trace file generated.

Refer asktom to view brief of all the steps.