microsoft excel 2010 barcode generator Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition in Software

Generation Code 128 Code Set B in Software Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition

Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
Code-128 Encoder In None
Using Barcode creation for Software Control to generate, create Code-128 image in Software applications.
USS Code 128 Reader In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
IV Data Storage and Querying
Make Code 128 Code Set B In Visual C#.NET
Using Barcode maker for Visual Studio .NET Control to generate, create Code-128 image in VS .NET applications.
Make Code 128 In VS .NET
Using Barcode drawer for ASP.NET Control to generate, create Code 128 Code Set B image in ASP.NET applications.
14 Query Optimization
Painting Code 128 In .NET
Using Barcode maker for Visual Studio .NET Control to generate, create Code128 image in Visual Studio .NET applications.
Code 128 Code Set C Generator In VB.NET
Using Barcode drawer for .NET Control to generate, create Code128 image in Visual Studio .NET applications.
The McGraw Hill Companies, 2001
Encoding Data Matrix In None
Using Barcode generation for Software Control to generate, create Data Matrix image in Software applications.
Painting ANSI/AIM Code 39 In None
Using Barcode printer for Software Control to generate, create Code-39 image in Software applications.
Transformation of Relational Expressions
Generate UPC-A Supplement 5 In None
Using Barcode creator for Software Control to generate, create UPCA image in Software applications.
Barcode Printer In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
There are other options to consider for evaluating our query We do not care about the order in which attributes appear in a join, since it is easy to change the order before displaying the result Thus, for all relations r1 and r2 , r1
Bar Code Encoder In None
Using Barcode creator for Software Control to generate, create bar code image in Software applications.
Make Code 128 Code Set B In None
Using Barcode creation for Software Control to generate, create Code 128 Code Set C image in Software applications.
r2 = r2
USD - 8 Generator In None
Using Barcode encoder for Software Control to generate, create USD8 image in Software applications.
Barcode Drawer In Java
Using Barcode drawer for Android Control to generate, create bar code image in Android applications.
That is, natural join is commutative (equivalence rule 5) Using the associativity and commutativity of the natural join (rules 5 and 6), we can consider rewriting our relational-algebra expression as customer -name ((( branch -city = Brooklyn (branch)) 1 depositor) 1 account) That is, we could compute ( branch -city = Brooklyn (branch)) 1 depositor rst, and, after that, join the result with account Note, however, that there are no attributes in common between Branch-schema and Depositor-schema, so the join is just a Cartesian product If there are b branches in Brooklyn and d tuples in the depositor relation, this Cartesian product generates b d tuples, one for every possible pair of depositor tuple and branches (without regard for whether the account in depositor is maintained at the branch) Thus, it appears that this Cartesian product will produce a large temporary relation As a result, we would reject this strategy However, if the user had entered the preceding expression, we could use the associativity and commutativity of the natural join to transform this expression to the more ef cient expression that we used earlier
Bar Code Drawer In .NET
Using Barcode drawer for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Code 3 Of 9 Drawer In Java
Using Barcode creation for Java Control to generate, create Code 39 Extended image in Java applications.
1434 Enumeration of Equivalent Expressions
GTIN - 13 Creator In Objective-C
Using Barcode generation for iPad Control to generate, create EAN 13 image in iPad applications.
Create ECC200 In Visual C#
Using Barcode printer for Visual Studio .NET Control to generate, create ECC200 image in .NET framework applications.
Query optimizers use equivalence rules to systematically generate expressions equivalent to the given query expression Conceptually, the process proceeds as follows Given an expression, if any subexpression matches one side of an equivalence rule, the optimizer generates a new expression where the subexpression is transformed to match the other side of the rule This process continues until no more new expressions can be generated The preceding process is costly both in space and in time Here is how the space requirement can be reduced: If we generate an expression E1 from an expression E2 by using an equivalence rule, then E1 and E2 are similar in structure, and have subexpressions that are identical Expression-representation techniques that allow both expressions to point to shared subexpressions can reduce the space requirement signi cantly, and many query optimizers use them Moreover, it is not always necessary to generate every expression that can be generated with the equivalence rules If an optimizer takes cost estimates of evaluation into account, it may be able to avoid examining some of the expressions, as we shall see in Section 144 We can reduce the time required for optimization by using techniques such as these
Draw UPC-A Supplement 5 In Objective-C
Using Barcode creator for iPhone Control to generate, create UPCA image in iPhone applications.
Recognizing Barcode In Visual Basic .NET
Using Barcode Control SDK for .NET framework Control to generate, create, read, scan barcode image in Visual Studio .NET applications.
Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
IV Data Storage and Querying
14 Query Optimization
The McGraw Hill Companies, 2001
14
Query Optimization
144 Choice of Evaluation Plans
Generation of expressions is only part of the query-optimization process, since each operation in the expression can be implemented with different algorithms An evaluation plan is therefore needed to de ne exactly what algorithm should be used for each operation, and how the execution of the operations should be coordinated Figure 144 illustrates one possible evaluation plan for the expression from Figure 143 As we have seen, several different algorithms can be used for each relational operation, giving rise to alternative evaluation plans Further, decisions about pipelining have to be made In the gure, the edges from the selection operations to the merge join operation are marked as pipelined; pipelining is feasible if the selection operations generate their output sorted on the join attributes They would do so if the indices on branch and account store records with equal values for the index attributes sorted by branch-name
1441 Interaction of Evaluation Techniques
One way to choose an evaluation plan for a query expression is simply to choose for each operation the cheapest algorithm for evaluating it We can choose any ordering of the operations that ensures that operations lower in the tree are executed before operations higher in the tree However, choosing the cheapest algorithm for each operation independently is not necessarily a good idea Although a merge join at a given level may be costlier than a hash join, it may provide a sorted output that makes evaluating a later operation (such as duplicate elimination, intersection, or another merge join) cheaper Similarly, a nested-loop join with indexing may provide opportunities for pipelining the results to the next operation, and thus may be useful even if it is not the cheapest way of
customer-name (sort to remove duplicates) (hash join)
Copyright © OnBarcode.com . All rights reserved.