cost-based query optimization consist ofSelect one:a.Annotate resultant expressions to get alternative query plansb.Generating logically equivalent expressions using equivalence rulesc.Choose the cheapest plan based on estimated costd.All of the above

In Query optimization, Estimation of plan cost is based on:Select one:a.Statistics estimation for intermediate results to compute cost of complex expressionsb.All of the abovec.Cost formulae for algorithms, computed using statisticsd.Statistical information about relations

What is TRUE about Query Optimization?Select one:a. All of the aboveb.The cost of evaluating a query can vary depending on its type.c.The evaluation plan is built by the system, so the user need not focus on writing their query efficiently.d.An efficient query evaluation plan is generated by a database system, which minimizes its costs.

A query execution plan provides crucial assistance for query optimization by showing the following elements:Select THREE.A. Join typeB. Alternative (more suitable) join conditionC. Estimated query costD. NO STATISTICS indicator

You are comparing two query execution plans.Query plan A has an estimated query cost of 1000Query plan B has an estimated query cost of 500What can we conclude from this?A.Query B will take 50% less time to execute than query AB.Query B is more efficient but that has no impact on query execution timeC.Query A is less efficient and most likely slower than a query B.

Heuristic optimization transforms the query-tree by using a set of rules that typically (but not in all cases) improve execution performance .It uses which rules to do soSelect one:a.Perform projection early (reduces the number of attributes)b.Perform most restrictive selection and join operations (i.e., with smallest result size) before other similar operations.c. All of the aboved.Perform selection early (reduces the number of tuples)