Multi-Column Statistics in Java

Generator ECC200 in Java Multi-Column Statistics
Multi-Column Statistics
Data Matrix 2d Barcode Generator In Java
Using Barcode printer for Java Control to generate, create DataMatrix image in Java applications.
Histograms are for columns, not combinations of columns Even if you have a multi-column compound index, the DBMS will prefer to calculate full histograms for the first column only
Create Barcode In Java
Using Barcode generation for Java Control to generate, create bar code image in Java applications.
EXPLAIN
Scanning Barcode In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
The non-standard EXPLAIN statement (see Table 17-1) is the vital way to find out what the optimizer has done We haven't mentioned it up to now because this book's primary goal has been to show what you can do before the fact But EXPLAIN is the way to measure whether your estimates correspond to DBMS reality In many shops, it's customary to get an EXPLAIN for every SQL statement before submitting it for execution That is quite reasonable What's perhaps less reasonable is the custom of trying out every transformation one can think of and submitting them all for explanation That is mere floundering Understanding principles in other words, estimating what's best before the fact is more reliable and less time consuming So don't flounder read this book! Here is an example of a typical EXPLAIN output, from Informix:
DataMatrix Creator In C#
Using Barcode creator for VS .NET Control to generate, create Data Matrix image in .NET applications.
SET EXPLAIN ON QUERY: SELECT column1, column2 FROM Table1; Estimated cost: 3 Estimated # of rows returned: 50 1) Owner1Table1 : SEQUENTIAL SCAN
Printing Data Matrix In .NET Framework
Using Barcode generation for ASP.NET Control to generate, create Data Matrix 2d barcode image in ASP.NET applications.
With most DBMSs, the EXPLAIN result goes to a table or file so you can select the information you need In many cases, the EXPLAIN statement's output is much harder to follow than the short example we show here, which is why graphic tools like IBM's Visual EXPLAIN are useful
Data Matrix 2d Barcode Generation In .NET
Using Barcode printer for VS .NET Control to generate, create Data Matrix ECC200 image in .NET framework applications.
Hints
Data Matrix 2d Barcode Encoder In Visual Basic .NET
Using Barcode encoder for VS .NET Control to generate, create ECC200 image in Visual Studio .NET applications.
Most DBMSs provide some non-standard way to override the optimizer if you judge that its estimates or formulas are wrong Commonly the mechanism is a hint, which often looks like a comment or parenthetical clause in the SQL statement but in fact is a direction to the optimizer Here's an example from Oracle:
Generating Barcode In Java
Using Barcode maker for Java Control to generate, create barcode image in Java applications.
SELECT /*+ INDEX(Table1 Index1) */ column1, column2 FROM Table1 WHERE column1 >55
ANSI/AIM Code 39 Encoder In Java
Using Barcode encoder for Java Control to generate, create USS Code 39 image in Java applications.
And here's one from Sybase:
GTIN - 128 Generator In Java
Using Barcode creation for Java Control to generate, create EAN / UCC - 14 image in Java applications.
SELECT column1, column2 FROM Table1 (INDEX Index1 PREFETCH 16) WHERE column1 > 55
Making Bar Code In Java
Using Barcode encoder for Java Control to generate, create bar code image in Java applications.
Hints are important enough to warrant mention, but there is no such thing as a portable hint; every DBMS (except IBM) has its own optimizer-specific hint set We'll therefore limit ourselves to listing the most common hints, without getting into syntax
Draw GS1 - 12 In Java
Using Barcode generation for Java Control to generate, create UPC Code image in Java applications.
The predicate that follows is probably true Stop trying to optimize if time-to-estimate is greater than time-to-execute Use rule-based optimizer instead of cost-based optimizer Prefer index X on table Y
C 2 Of 5 Maker In Java
Using Barcode printer for Java Control to generate, create Code 2 of 5 image in Java applications.
DBA note: Administrators can influence some DBMS's plans more generally with a manual override of the statistics, for example, by declaring that the selectivity of an index is 80% rather than 40%
Decode EAN13 In Visual Studio .NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
Parting Shots
Barcode Maker In VS .NET
Using Barcode generator for Visual Studio .NET Control to generate, create bar code image in Visual Studio .NET applications.
After getting through the earlier chapters of this book, you're aware to a more or less painful degree that many optimizations are your responsibility This last chapter has been a bit of good news: you have an ally Until a few years ago, many DBMS optimizers were weak because they took only static information into account Nowadays, optimizers are more useful because they also take dynamic datarelated information into account Perhaps soon the next phase will come, and optimizers will take user activity into account as well Certainly, no optimizer can guarantee that the access plan it chooses will be perfect every time, but there's such a thing as progress We salute the DBMSs that we have been discussing for so long
Data Matrix 2d Barcode Generator In C#
Using Barcode generation for Visual Studio .NET Control to generate, create Data Matrix ECC200 image in VS .NET applications.
Appendix A Further Reading
Barcode Drawer In Visual C#
Using Barcode encoder for VS .NET Control to generate, create barcode image in .NET applications.
Bowman, Judith Practical SQL: The Sequel Boston: Addison-Wesley, 2000 Celko, Joe SQL for Smarties: Advanced SQL Programming San Francisco: Morgan Kaufmann Publishers, 2000 Delaney, Kalen Inside Microsoft SQL Server 2000 Redmond, WA: Microsoft Press, 2000 Dewdney, A K "On the spaghetti computer and other analog gadgets for problem solving" Scientific American 19 (June 1984) DuBois, Paul MySQL Indianapolis: New Riders Publishing, 1999 Flannery, Ron Informix Handbook Upper Saddle River, NJ: Prentice Hall PTR, 2000 Gulutzan, Peter, and Trudy Pelzer SQL-99 Complete, Really Lawrence, KS: R&D Books, 1999 International Organization for Standardization Database Language SQL ISO/IEC 9075-1:1999 (SQL/Framework) International Organization for Standardization Database Language SQL ISO/IEC 9075-2:1999 (SQL/Foundation)
Data Matrix ECC200 Decoder In VS .NET
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in .NET applications.
International Organization for Standardization Database Language SQL ISO/IEC 9075-3:1999 (SQL/CLI) International Organization for Standardization Database Language SQL ISO/IEC 9075-4:1999 (SQL/PSM) Kline, Kevin, Lee Gould, and Andrew Zanevsky Transact-SQL Programming Sebastopol: O'Reilly & Associates, 1999 Kyte, Thomas Expert One on One: Oracle Chicago: Wrox Press, 2001 Loney, Kevin, and George Koch Oracle8i: The Complete Reference Berkeley: Osborne McGrawHill, 2000 Mullins, Craig DB2 Developer's Guide Indianapolis: SAMS Publishing, 2000 North, Ken Database Magic with Ken North Upper Saddle River, NJ: Prentice Hall PTR, 1998 Orfali, Robert, and Dan Harkey Client/server programming with Java and CORBA New York: Wiley Computer Press, 1997 White, Seth, Maydene Fisher, Rick Cattell, Graham Hamilton, and Mark Hapner JDBC API Tutorial and Reference, 2d ed Boston: Addison-Wesley, 1999 Yevich, Richard, and Susan Lawson DB2 High Performance Design and Tuning Upper Saddle River, NJ: Prentice Hall PTR, 2000
Printing UPC-A Supplement 5 In .NET Framework
Using Barcode drawer for ASP.NET Control to generate, create UPC-A image in ASP.NET applications.
Bar Code Drawer In Visual Basic .NET
Using Barcode encoder for .NET framework Control to generate, create barcode image in .NET framework applications.