barcode generator in vb.net code project SQL: A Beginner s Guide in Software

Encoding Code 39 Extended in Software SQL: A Beginner s Guide

SQL: A Beginner s Guide
ANSI/AIM Code 39 Decoder In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Create Code 39 In None
Using Barcode generation for Software Control to generate, create ANSI/AIM Code 39 image in Software applications.
True
USS Code 39 Scanner In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
Generating Code 39 Full ASCII In C#
Using Barcode generator for .NET framework Control to generate, create Code 39 Extended image in VS .NET applications.
True False Unknown True True True
Code 39 Maker In .NET Framework
Using Barcode drawer for ASP.NET Control to generate, create ANSI/AIM Code 39 image in ASP.NET applications.
Code39 Printer In VS .NET
Using Barcode generation for .NET framework Control to generate, create Code-39 image in VS .NET applications.
False
Print Code 3/9 In Visual Basic .NET
Using Barcode drawer for .NET Control to generate, create Code 39 image in VS .NET applications.
Making Data Matrix In None
Using Barcode printer for Software Control to generate, create Data Matrix image in Software applications.
True False Unknown
Code128 Encoder In None
Using Barcode creator for Software Control to generate, create Code 128C image in Software applications.
Generate UCC - 12 In None
Using Barcode drawer for Software Control to generate, create UPC A image in Software applications.
Unknown
Generating EAN-13 Supplement 5 In None
Using Barcode creation for Software Control to generate, create EAN13 image in Software applications.
Making GTIN - 128 In None
Using Barcode maker for Software Control to generate, create GS1 128 image in Software applications.
True Unknown Unknown
Print RM4SCC In None
Using Barcode printer for Software Control to generate, create British Royal Mail 4-State Customer Barcode image in Software applications.
Encode Barcode In None
Using Barcode drawer for Online Control to generate, create bar code image in Online applications.
Table 7-1 Evaluating Predicates Connected by OR
GTIN - 128 Generator In VB.NET
Using Barcode creator for Visual Studio .NET Control to generate, create EAN / UCC - 13 image in .NET applications.
Matrix Barcode Maker In VB.NET
Using Barcode maker for Visual Studio .NET Control to generate, create Matrix 2D Barcode image in VS .NET applications.
As the table shows, if both predicates evaluate to true, then the search condition evaluates to true. If both are false, then the search condition evaluates to false. A condition is provided for each possible match. For example, suppose your SELECT statement includes the following WHERE clause:
Paint Code39 In Objective-C
Using Barcode drawer for iPad Control to generate, create Code-39 image in iPad applications.
Draw 2D Barcode In Java
Using Barcode creator for Java Control to generate, create Matrix Barcode image in Java applications.
WHERE PERFORMER_TYPE = 'Folk' OR PERFORMER_TYPE = 'Jazz'
Code 39 Full ASCII Recognizer In Visual C#.NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
Decoding Code 128 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
Now suppose that the first predicate in this example (PERFORMER_TYPE = Folk ) evaluates to true and the second predicate (PERFORMER_TYPE = Jazz ) evaluates to false. This means that the row being evaluated contains the Folk value in the PERFORMER_TYPE column, but does not contain the Jazz value in that column. Now refer back to Table 7-1. If you select True from the first column, select False from the top row, and then match these two values together (by picking where they intersect), you can see that the search condition evaluates to true, so the row will be included in the query results. You can do the same thing with the AND keyword as you did with the OR keyword. Table 7-2 matches the nine possible outcomes of two predicates. Again, you simply match up how each predicate is evaluated to determine whether the search condition will be evaluated to true, false, or unknown. Remember, the search condition must evaluate to true for the row to be included in the query results. As you can see, the AND keyword is a lot less forgiving than the OR keyword. The only way for the search condition to evaluate to true is for both predicates to evaluate to true.
True
True False Unknown True False Unknown
False
False False False
Unknown
Unknown False Unknown
Table 7-2 Evaluating Predicates Connected by AND
7:
Querying SQL Data
NOTE
Comparison operators and predicates in general are discussed in greater detail in 9.
If a search condition includes more than two predicates, the predicates are evaluated in an order chosen by the RDBMS, unless parentheses are used to separate combinations of predicates. While the SQL standard does not specify the order in which multiple predicates are to be evaluated, most RDBMS products evaluate AND before OR. For example, you might have a SELECT statement that includes the following WHERE clause:
WHERE IN_STOCK = 6 OR IN_STOCK = 27 AND LABEL_ID = 833 OR LABEL_ID = 829
Notice that there are four predicates in this clause and no parentheses. Assuming that AND is evaluated before OR, the above WHERE clause would be evaluated as if it was written this way:
WHERE IN_STOCK = 6 OR (IN_STOCK = 27 AND LABEL_ID = 833) OR LABEL_ID = 829
In order to evaluate to true, a row must contain one of the following values or set of values:
IN_STOCK value of 6 IN_STOCK value of 27 and LABEL_ID value of 833 LABEL_ID value of 829
When you include both the AND and OR keywords in the same WHERE clause, it is always a good idea to include parentheses to make sure you are getting the filtering you intend, keeping in mind that predicates within parentheses are always evaluated first. If the RDBMS makes other assumptions, or if parentheses are used around other sets of predicates, the results will be different from what we ve seen. For example, suppose you use parentheses as follows:
WHERE (IN_STOCK = 6 OR IN_STOCK = 27) AND (LABEL_ID = 833 OR LABEL_ID = 829)
The predicates are first evaluated within the context of the parentheses and then compared to other predicates accordingly. In this case, a row must contain one of the two IN_STOCK values and the row must contain one of the two LABEL_ID values. As a result, a row must contain one of the following sets of values to evaluate to true:
IN_STOCK value of 6 and LABEL_ID value of 833 IN_STOCK value of 6 and LABEL_ID value of 829 IN_STOCK value of 27 and LABEL_ID value of 833 IN_STOCK value of 27 and LABEL_ID value of 829
SQL: A Beginner s Guide
NOTE
SQL includes three operators that you can use if a search condition becomes too complicated. These operators are IS TRUE, IS FALSE, and IS UNKNOWN. For example, you can specify the following search condition: (FIRST_NAME = Joni AND LAST_ NAME = Mitchell ) IS TRUE. This means that the FIRST_NAME value of a returned row must be Joni and the LAST_NAME value must be Mitchell. In other words, they must evaluate to true. If you specify IS FALSE in this situation, the predicate pair would have to evaluate to false, meaning that at least one of the two predicates had to be false (could not be Joni or could not be Mitchell).
Another keyword that you might find useful is the NOT keyword, which can be used alone or along with the AND keyword and the OR keyword to specify the inverse of a predicate. For example, your SELECT statement might include the following WHERE clause:
WHERE PERFORMER_NAME = 'Joni Mitchell' OR NOT PERFORMER_NAME = 'Kitaro'
In this case, the PERFORMER_NAME value can be Joni Mitchell or it can be any value other than Kitaro. Of course, Joni Mitchell is not equal to Kitaro, so that predicate is redundant and you get the same result if you remove it. Furthermore, you would get the same result if you used the not equal (<>) comparison operator, so the entire WHERE clause can be rewritten more simply as:
WHERE PERFORMER_NAME <> 'Kitaro'
Copyright © OnBarcode.com . All rights reserved.