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c# generate barcode CH A PT ER 1 0 H O W TO A PPRO A CH A Q UERY in Font
CH A PT ER 1 0 H O W TO A PPRO A CH A Q UERY PDF417 Printer In None Using Barcode maker for Font Control to generate, create PDF-417 2d barcode image in Font applications. www.OnBarcode.comMake Universal Product Code Version A In None Using Barcode printer for Font Control to generate, create GS1 - 12 image in Font applications. www.OnBarcode.comOnce we have the view AllTourInfo, it can be used in the same way as any other table in our queries. To find the names of men who have entered a Leeston tournament, we can use the view as shown in Listing 10-8. Code 128 Code Set B Creation In None Using Barcode printer for Font Control to generate, create Code 128 image in Font applications. www.OnBarcode.comEncoding European Article Number 13 In None Using Barcode generator for Font Control to generate, create EAN-13 image in Font applications. www.OnBarcode.comListing 10-8. Retrieving the Names of Men Who Have Entered a Leeston Tournament Using
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Encoding Barcode In Objective-C Using Barcode drawer for iPhone Control to generate, create Barcode image in iPhone applications. www.OnBarcode.comEncoding GS1 128 In Java Using Barcode printer for Android Control to generate, create USS-128 image in Android applications. www.OnBarcode.comThe big picture approach assumes that you have decided how to combine the tables that will contribute to the query. Sometimes, you will think it is obvious that, for example, you need to join the tables. Other times, it may not be at all clear initially. In this section, we will look at some key words that often appear in questions and that can provide a clue about which relational operations you will need. If none of these help, remember that we still have the No Idea Where to Start section coming up! Barcode Drawer In Java Using Barcode generation for Java Control to generate, create Barcode image in Java applications. www.OnBarcode.comBarcode Encoder In Java Using Barcode drawer for Java Control to generate, create Barcode image in Java applications. www.OnBarcode.comAnd, Both, Also
Generating QR Code In Java Using Barcode generation for Java Control to generate, create Denso QR Bar Code image in Java applications. www.OnBarcode.comUSS-128 Creation In Objective-C Using Barcode generator for iPhone Control to generate, create EAN128 image in iPhone applications. www.OnBarcode.com And and also can be tricky words when it comes to interpreting queries, and we will consider this further in the next chapter. In this section, we will look at queries that have the idea of two conditions needing to be met simultaneously. Queries that require two conditions to be met fall into two sorts: those that can be carried out with a simple WHERE clause containing AND and those that require an intersection or self join. To decide if a query really needs two conditions to be met, I usually look at a naturallanguage statement and see if I can reword it with the word both connecting the conditions. Consider these examples: Find the junior boys. (Both a male and a junior Yes.) Find those members who entered tournaments 24 and 38. (Both tournaments Yes.) Find the women and children. (Both a female and a child No.) The last query is the one that can trick you. Although it contains the word and, the common interpretation of women and children doesn t mean someone who is both a female and a child (that is, a girl). Rather, the phrase means anyone who is either a female or a child (especially when populating lifeboats). GTIN - 128 Maker In .NET Using Barcode creator for Reporting Service Control to generate, create GS1-128 image in Reporting Service applications. www.OnBarcode.comBarcode Creator In Objective-C Using Barcode generation for iPad Control to generate, create Barcode image in iPad applications. www.OnBarcode.comCHAPTER 10 HOW TO APPROAC H A QUERY
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Children
Females
Children
a) Either condition (Women and children) b) Both conditions ( Girls ) Figure 10-8. Visualizing if two conditions both need to be met
When two conditions must be met, we are looking at the intersection of two groups of data, as in the diagram in Figure 10-8b. If we have a query that requires an intersection, that doesn t necessarily mean we must use the INTERSECT keyword. I find the following question helpful in deciding what to do next: Do I need to look at more than one row to decide if both conditions are satisfied Consider the query to find junior boys. This is going to need the Member table. Can we look at a single row and determine if the member is both a junior and a boy As we can see in Figure 10-9, it is possible to determine both these conditions from a single row. Figure 10-9. We can investigate both conditions by looking at a single row.
CH A PT ER 1 0 H O W TO A PPRO A CH A Q UERY
In this situation, we can use a simple select operation with the Boolean AND to check for both conditions. This is discussed in 2, and the SQL is shown in Listing 10-9. Listing 10-9. Both Conditions Can Be Checked in a Single WHERE Clause SELECT * FROM Member m WHERE m.Gender = 'M' AND m.MemberType = 'Junior' Now consider a different type of query. What about finding the members who have entered both tournaments 24 and 36 To do this, we need to look at the Entry table (probably joined with the Member table if we want the names). As we can see in Figure 10-10, we cannot check that a member has entered both tournaments by looking at a single row.
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