generate barcode vb.net SET OPERATIONS AND DISTINCT in Java

Encode Code 39 in Java SET OPERATIONS AND DISTINCT

SET OPERATIONS AND DISTINCT
Generating ANSI/AIM Code 39 In Java
Using Barcode maker for Java Control to generate, create Code 39 image in Java applications.
www.OnBarcode.com
Scan ANSI/AIM Code 39 In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Contrary to the received wisdom on set operations, it seems that the practice of omitting the distinct operator is actually a bad idea the optimizer does a better job of estimating the cardinality of the base result set if you include the distinct. It shouldn t matter, but at present it does.
Printing Code 128B In Java
Using Barcode generation for Java Control to generate, create Code 128A image in Java applications.
www.OnBarcode.com
GS1 128 Encoder In Java
Using Barcode generator for Java Control to generate, create EAN / UCC - 14 image in Java applications.
www.OnBarcode.com
When it comes to the cardinality of the result from the set operator itself, we are back on familiar territory. Running the tests under 10g, I got the following sets of figures shown in Table 13-8. As you can see, once the optimizer has worked out the cardinalities of the base queries, it uses a worst-case scenario to work out the results of the set operation.
EAN / UCC - 14 Drawer In Java
Using Barcode drawer for Java Control to generate, create EAN 128 image in Java applications.
www.OnBarcode.com
Drawing GS1 - 12 In Java
Using Barcode generator for Java Control to generate, create GS1 - 12 image in Java applications.
www.OnBarcode.com
CHAPTER 13 SORTING AND MERGE JOINS
Make ECC200 In Java
Using Barcode maker for Java Control to generate, create Data Matrix ECC200 image in Java applications.
www.OnBarcode.com
British Royal Mail 4-State Customer Code Maker In Java
Using Barcode generation for Java Control to generate, create Royal Mail Barcode image in Java applications.
www.OnBarcode.com
Table 13-8. Cardinality Methods for Sets Operators
Creating Code 3 Of 9 In Objective-C
Using Barcode creator for iPhone Control to generate, create Code 39 Extended image in iPhone applications.
www.OnBarcode.com
Reading Code 39 In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Data Set
UPCA Maker In .NET Framework
Using Barcode encoder for VS .NET Control to generate, create UPC-A Supplement 5 image in .NET applications.
www.OnBarcode.com
Printing EAN13 In None
Using Barcode creation for Excel Control to generate, create EAN-13 image in Microsoft Excel applications.
www.OnBarcode.com
t1 t2 union intersect minus
Draw QR Code In None
Using Barcode printer for Microsoft Word Control to generate, create QR Code image in Office Word applications.
www.OnBarcode.com
Barcode Printer In Java
Using Barcode generation for BIRT reports Control to generate, create Barcode image in BIRT applications.
www.OnBarcode.com
Group Cardinality
Print EAN / UCC - 14 In None
Using Barcode creation for Software Control to generate, create UCC-128 image in Software applications.
www.OnBarcode.com
GS1-128 Creation In .NET Framework
Using Barcode creator for Visual Studio .NET Control to generate, create USS-128 image in .NET framework applications.
www.OnBarcode.com
20 15 35 15 20
Scan Code 128B In VS .NET
Using Barcode recognizer for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
Barcode Encoder In .NET Framework
Using Barcode generator for ASP.NET Control to generate, create Barcode image in ASP.NET applications.
www.OnBarcode.com
Reason
PDF-417 2d Barcode Scanner In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Create Code 128 Code Set A In .NET Framework
Using Barcode creator for ASP.NET Control to generate, create Code-128 image in ASP.NET applications.
www.OnBarcode.com
owner (4) * object_type (7) / 1.4142 owner (3) * object_type (7) / 1.4142 t1 value + t2 value least (t1 value, t2 value) First (i.e., t1) value
You have to be a little careful with the assumptions you make about how the SQL will be operated. It is possible for things to change, and it may well have been true that in 8.0 or 7.3 the presence of the apparently redundant distinct would have resulted in an extra pair of sorts taking place. Things do change, and bugs can appear. If you look in the 10053 trace, by the way, you won t find any information about the set operation itself there will be a section for each of the two separate queries, followed by a final cost that represents the set operation. But there is no explanation or justification for the final figures. So you can only assume, as I do, that the optimizer just adds the cost of the separate queries to get the final cost of the set operation. Consider, as a final warning then, the following CTAS (which also appears in script set_ops.sql in the online code suite): create table t_intersect as select distinct * from ( select owner, object_type from t1 intersect select owner, object_type from t2 ) ; Clearly, the distinct in the outer select statement is redundant but we have already seen that Oracle is very good at avoiding sorts that are not really needed (not just in set operations, but also in our earlier example that featured a group by followed by an order by). So what s the execution plan for the CTAS Here s the output from dbms_xplan in 9.2.0.6 with CPU costing enabled: --------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| --------------------------------------------------------------------------| 0 | CREATE TABLE STATEMENT | | 2000 | 56000 | 16 (25)| | 1 | LOAD AS SELECT | | | | | | 2 | VIEW | | 2000 | 56000 | | | 3 | INTERSECTION | | | | | | 4 | SORT UNIQUE | | 2500 | 30000 | 8 (25)| | 5 | TABLE ACCESS FULL | T1 | 2500 | 30000 | 7 (15)| | 6 | SORT UNIQUE | | 2000 | 26000 | 8 (25)| | 7 | TABLE ACCESS FULL | T2 | 2000 | 26000 | 7 (15)| ---------------------------------------------------------------------------
CHAPTER 13 SORTING AND MERGE JOINS
The optimizer has very cleverly noticed that the distinct was redundant: according to the execution plan, the result set from the in-line view in line 2 has not been sorted. And here s the 10g version of the plan again with CPU costing enabled: ------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------| 0 | CREATE TABLE STATEMENT | | 2000 | 56000 | 20 (15)| 00:00:01 | | 1 | LOAD AS SELECT | | | | | | | 2 | SORT UNIQUE | | 2000 | 56000 | 18 (17)| 00:00:01 | | 3 | VIEW | | 2000 | 56000 | 17 (12)| 00:00:01 | | 4 | INTERSECTION | | | | | | | 5 | SORT UNIQUE | | 2500 | 32500 | 7 (15)| 00:00:01 | | 6 | TABLE ACCESS FULL| T1 | 2500 | 32500 | 6 (0)| 00:00:01 | | 7 | SORT UNIQUE | | 2000 | 26000 | 7 (15)| 00:00:01 | | 8 | TABLE ACCESS FULL| T2 | 2000 | 26000 | 6 (0)| 00:00:01 | ------------------------------------------------------------------------------Notice the sort unique at line 2 It looks like 10g has reintroduced the redundant sort that 9i was smart enough to eliminate. Fortunately, we can always check up on the sorting that actually happens by enabling event 10032 and guess what the 9i execution plan is lying. The 10032 trace files from both 9i and 10g show the same characteristic pattern. And I ve printed an extract of the 10g trace here: Input records Output records Input records Output records Input records Output records Input records Output records Input records Output records Input records Output records 2000 9 2500 10 9 9 9 9 2500 10 2000 9 -- T1
Copyright © OnBarcode.com . All rights reserved.