c# generate barcode More Rows Than There Should Be in Font

Encoding PDF 417 in Font More Rows Than There Should Be

More Rows Than There Should Be
PDF 417 Maker In None
Using Barcode generator for Font Control to generate, create PDF-417 2d barcode image in Font applications.
www.OnBarcode.com
Generating UCC-128 In None
Using Barcode generation for Font Control to generate, create GS1-128 image in Font applications.
www.OnBarcode.com
It is often easier to spot extra rows than it is to notice that rows are missing from your query result. You only need to see one record that you weren t expecting, and you can concentrate on the different parts of your query to see where it failed to be excluded. Here are a couple of causes of extra rows.
Code 128A Drawer In None
Using Barcode maker for Font Control to generate, create ANSI/AIM Code 128 image in Font applications.
www.OnBarcode.com
USS Code 39 Maker In None
Using Barcode generation for Font Control to generate, create Code 39 Full ASCII image in Font applications.
www.OnBarcode.com
Did You Use NOT Instead of Difference
UPC A Drawer In None
Using Barcode printer for Font Control to generate, create GS1 - 12 image in Font applications.
www.OnBarcode.com
Draw EAN13 In None
Using Barcode printer for Font Control to generate, create EAN 13 image in Font applications.
www.OnBarcode.com
With questions containing the words not or never, a sure way to get extra rows is to use a selection condition instead of a difference operator in the query. We looked at this issue in 4. To recap, consider a question like Which members have never entered tournament 25 A common first attempt using a select condition is shown in Listing 11-23.
PDF 417 Creation In None
Using Barcode creation for Font Control to generate, create PDF-417 2d barcode image in Font applications.
www.OnBarcode.com
UPC-E Supplement 5 Generation In None
Using Barcode encoder for Font Control to generate, create UCC - 12 image in Font applications.
www.OnBarcode.com
CHAPTER 11 C OM MON PROBLE MS
Generating PDF-417 2d Barcode In .NET Framework
Using Barcode generation for ASP.NET Control to generate, create PDF-417 2d barcode image in ASP.NET applications.
www.OnBarcode.com
PDF 417 Generator In C#.NET
Using Barcode maker for .NET Control to generate, create PDF-417 2d barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Listing 11-23. First Attempt at Finding Members Who Have Not Entered Tournament 25 SELECT * FROM Entry WHERE TourID <> 25
Decode PDF417 In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Draw EAN-13 In None
Using Barcode maker for Software Control to generate, create EAN / UCC - 13 image in Software applications.
www.OnBarcode.com
The condition in the WHERE clause checks rows one at a time to see if they should be included in the result. If there is a row for member 415 entering tournament 36, then that row will be retrieved, regardless of the possibility that another row shows member 415 entered tournament 25. For example, if member 415 has entered tournament 25 and four other tournaments, we will retrieve four rows when we were expecting none. The correct query for this type of question is to use a nested query (see 4) or the EXCEPT difference operator (see 7). We need to find the set of all members (from the Member table) and remove the set of members who have entered tournament 25 (from the Entry table). Listings 11-24 and 11-25 show two possibilities.
Create Barcode In None
Using Barcode drawer for Word Control to generate, create Barcode image in Word applications.
www.OnBarcode.com
Generate GS1-128 In Objective-C
Using Barcode generator for iPad Control to generate, create UCC - 12 image in iPad applications.
www.OnBarcode.com
Listing 11-24. Finding Members Who Have Not Entered Tournament 25 with a Nested Query SELECT MemberID FROM Member WHERE MemberID NOT IN (SELECT MemberID FROM Entry WHERE TourID = 25) Listing 11-25. Finding Members Who Have Not Entered Tournament 25 with a Difference Operator SELECT MemberID FROM Member EXCEPT SELECT MemberID FROM Entry WHERE TourID = 25
Linear 1D Barcode Drawer In .NET Framework
Using Barcode generator for ASP.NET Control to generate, create Linear 1D Barcode image in ASP.NET applications.
www.OnBarcode.com
Generate Barcode In Objective-C
Using Barcode creation for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
Have You Dealt with Duplicates Appropriately
UCC-128 Creation In Java
Using Barcode creation for Java Control to generate, create USS-128 image in Java applications.
www.OnBarcode.com
Generating European Article Number 13 In Java
Using Barcode creator for Java Control to generate, create UPC - 13 image in Java applications.
www.OnBarcode.com
It sometimes takes a little thought to decide what needs to be done with duplicate records retrieved from a query. By default, SQL will retain all duplicates. The following two requests sound similar: Give me a list of the names of my customers. Give me a list of the cities my customers live in. In the first, we probably expect as many rows as we have customers; if we have several Johns, we expect them all to be retained. In the second, if we have 500 customers living in Christchurch, we don t expect 500 rows to be returned. In the query to find the cities, we want only the distinct values. Listing 11-26 shows how to use the DISTINCT keyword.
UCC - 12 Generation In None
Using Barcode drawer for Software Control to generate, create GTIN - 12 image in Software applications.
www.OnBarcode.com
Draw PDF-417 2d Barcode In Java
Using Barcode generator for Java Control to generate, create PDF 417 image in Java applications.
www.OnBarcode.com
C HA PTER 11 C OMMON PROBLEMS
Listing 11-26. Finding the Cities Where Customers Reside SELECT DISTINCT (City) FROM Customer
Statistics or Aggregates Incorrect
All of the preceding problems can cause incorrect statistics. If you are counting, grouping, or averaging, and your underlying query misses rows or returns extra rows, then clearly the statistics will be affected. A couple of other things to consider are how Nulls and duplicates are being handled. SQL will not include any Null fields in its statistics. For example, COUNT(Handicap) or AVG(Handicap) will ignore any rows with Nulls in the Handicap field. It is also important to consider what you want done with duplicates, especially for counting functions. COUNT(Handicap) will return the number of members who have a value in the Handicap column. COUNT(DISTINCT Handicap) will return the number of different values in the Handicap column if all the members have a handicap of 20, it will return a count of 1.
The Order Is Wrong
If you have used an ORDER BY clause in your query and you are having problems with the order in which the rows are being presented, there is often a problem with the underlying data. Review the Problems with Data Values section earlier in this chapter. Check that the field types are appropriate (for example, numeric values aren t being stored in text fields) and that text values have consistent case and no extraneous characters.
Copyright © OnBarcode.com . All rights reserved.