Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition in Software

Paint USS Code 128 in Software Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition

Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
Code 128 Code Set B Generation In None
Using Barcode encoder for Software Control to generate, create Code 128 Code Set C image in Software applications.
Decoding Code-128 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
IV Data Storage and Querying
Code 128 Generator In Visual C#.NET
Using Barcode maker for .NET Control to generate, create USS Code 128 image in .NET framework applications.
Making Code 128C In VS .NET
Using Barcode generator for ASP.NET Control to generate, create Code 128C image in ASP.NET applications.
13 Query Processing
ANSI/AIM Code 128 Generation In .NET
Using Barcode creation for .NET framework Control to generate, create Code 128A image in Visual Studio .NET applications.
Code 128 Drawer In VB.NET
Using Barcode creation for Visual Studio .NET Control to generate, create Code 128A image in .NET applications.
The McGraw Hill Companies, 2001
UPC - 13 Drawer In None
Using Barcode creation for Software Control to generate, create GS1 - 13 image in Software applications.
Print Bar Code In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
Selection Operation
GS1-128 Printer In None
Using Barcode creator for Software Control to generate, create EAN128 image in Software applications.
Generate GTIN - 12 In None
Using Barcode generator for Software Control to generate, create UPC-A Supplement 5 image in Software applications.
all tuples that satisfy the condition For A > v, the le scan starts with the rst tuple such that A > v For comparisons of the form A < v or A v, an index lookup is not required For A < v, we use a simple le scan starting from the beginning of the le, and continuing up to (but not including) the rst tuple with attribute A = v The case of A v is similar, except that the scan continues up to (but not including) the rst tuple with attribute A > v In either case, the index is not useful A7 (secondary index, comparison) We can use a secondary ordered index to guide retrieval for comparison conditions involving <, , , or > The lowestlevel index blocks are scanned, either from the smallest value up to v (for < and ), or from v up to the maximum value (for > and ) The secondary index provides pointers to the records, but to get the actual records we have to fetch the records by using the pointers This step may require an I/O operation for each record fetched, since consecutive records may be on different disk blocks If the number of retrieved records is large, using the secondary index may be even more expensive than using linear search Therefore the secondary index should be used only if very few records are selected
Encoding Code 128A In None
Using Barcode creation for Software Control to generate, create Code-128 image in Software applications.
Data Matrix 2d Barcode Maker In None
Using Barcode encoder for Software Control to generate, create Data Matrix ECC200 image in Software applications.
1334 Implementation of Complex Selections
OneCode Printer In None
Using Barcode maker for Software Control to generate, create USPS OneCode Solution Barcode image in Software applications.
Draw EAN 128 In Objective-C
Using Barcode generator for iPhone Control to generate, create UCC-128 image in iPhone applications.
So far, we have considered only simple selection conditions of the form A op B, where op is an equality or comparison operation We now consider more complex selection predicates Conjunction: A conjunctive selection is a selection of the form 1 2 n (r) Disjunction: A disjunctive selection is a selection of the form 1 2 n (r) A disjunctive condition is satis ed by the union of all records satisfying the individual, simple conditions i Negation: The result of a selection (r) is the set of tuples of r for which the condition evaluates to false In the absence of nulls, this set is simply the set of tuples that are not in (r) We can implement a selection operation involving either a conjunction or a disjunction of simple conditions by using one of the following algorithms: A8 (conjunctive selection using one index) We rst determine whether an access path is available for an attribute in one of the simple conditions If one
Bar Code Encoder In Java
Using Barcode creation for Android Control to generate, create bar code image in Android applications.
Encode USS Code 128 In None
Using Barcode printer for Microsoft Excel Control to generate, create Code 128 Code Set A image in Microsoft Excel applications.
Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
UPC-A Supplement 2 Reader In .NET
Using Barcode scanner for .NET framework Control to read, scan read, scan image in .NET applications.
Draw Code 128 Code Set B In Visual Studio .NET
Using Barcode generator for ASP.NET Control to generate, create Code 128 Code Set A image in ASP.NET applications.
IV Data Storage and Querying
Printing European Article Number 13 In C#
Using Barcode maker for .NET framework Control to generate, create GS1 - 13 image in VS .NET applications.
Print Bar Code In Java
Using Barcode creation for Eclipse BIRT Control to generate, create barcode image in BIRT applications.
13 Query Processing
The McGraw Hill Companies, 2001
13
Query Processing
is, one of the selection algorithms A2 through A7 can retrieve records satisfying that condition We complete the operation by testing, in the memory buffer, whether or not each retrieved record satis es the remaining simple conditions To reduce the cost, we choose a i and one of algorithms A1 through A7 for which the combination results in the least cost for i (r) The cost of algorithm A8 is given by the cost of the chosen algorithm A9 (conjunctive selection using composite index) An appropriate composite index (that is, an index on multiple attributes) may be available for some conjunctive selections If the selection speci es an equality condition on two or more attributes, and a composite index exists on these combined attribute elds, then the index can be searched directly The type of index determines which of algorithms A3, A4, or A5 will be used A10 (conjunctive selection by intersection of identi ers) Another alternative for implementing conjunctive selection operations involves the use of record pointers or record identi ers This algorithm requires indices with record pointers, on the elds involved in the individual conditions The algorithm scans each index for pointers to tuples that satisfy an individual condition The intersection of all the retrieved pointers is the set of pointers to tuples that satisfy the conjunctive condition The algorithm then uses the pointers to retrieve the actual records If indices are not available on all the individual conditions, then the algorithm tests the retrieved records against the remaining conditions The cost of algorithm A10 is the sum of the costs of the individual index scans, plus the cost of retrieving the records in the intersection of the retrieved lists of pointers This cost can be reduced by sorting the list of pointers and retrieving records in the sorted order Thereby, (1) all pointers to records in a block come together, hence all selected records in the block can be retrieved using a single I/O operation, and (2) blocks are read in sorted order, minimizing disk arm movement Section 134 describes sorting algorithms A11 (disjunctive selection by union of identi ers) If access paths are available on all the conditions of a disjunctive selection, each index is scanned for pointers to tuples that satisfy the individual condition The union of all the retrieved pointers yields the set of pointers to all tuples that satisfy the disjunctive condition We then use the pointers to retrieve the actual records However, if even one of the conditions does not have an access path, we will have to perform a linear scan of the relation to nd tuples that satisfy the condition Therefore, if there is even one such condition in the disjunct, the most ef cient access method is a linear scan, with the disjunctive condition tested on each tuple during the scan The implementation of selections with negation conditions is left to you as an exercise (Exercise 1310)
Copyright © OnBarcode.com . All rights reserved.