Based on the discussion in Section 10.4.2, give a precise de?nition of when an access path covers the use of projection, union, and set-di?erence operators.
What will be an ideal response?
1. Consider a relational expression of the form ?attr1,...,attrn(R).
The use of projection operator is covered by an access path if and only if one of the following conditions holds:
a. The access path is ?le scan.
b. The access path is a hash index whose search key is a subset of the attributes attr1, ...,attrn.
c. The access path is a B+ tree index with the search key sk1,...,skm and some pre?x sk1,...,ski of that search key is a subset of attr1,...,attrn.
d. The access path is binary search and the relation R is sorted on the attributes sk1,...,skm. The de?nition of “covering” in this case is the same as for B+ tree indices.
2. Consider relational expressions of the form R ? S or R ? S. The use of union or set-di?erence is covered by an access path if and only if one of the following conditions holds:
a. The access path is ?le scan.
b. The access path is a hash index on R and S.
c. The access path is a B+ tree index on R and S.
d. The access path is binary search and the relations R and S are sorted.
You might also like to view...
Match the following terms to their meanings: I. Grouping II. Order of operations III. Argument IV. Total Row V. Expression A. Data needed to produce the output for a function B. Consist of different elements to produce the desired output C. Summarizes data by the values of a field D. Determines the sequence in which calculations are performed E. Displays results of aggregate functions in last row
in a Datasheet What will be an ideal response?
Using Comma Style causes a negative number to be displayed inside parentheses
Indicate whether the statement is true or false