By Clare Churcher
Clare Churcher's Beginning SQL Queries is your advisor to getting to know the lingua franca of the database undefined: the SQL language. strong wisdom of SQL is important to a person operating with databases, since it is with SQL that you just retrieve info, control info, and generate enterprise effects. realizing tips on how to write reliable queries is the basis for all paintings performed in SQL, and it's a beginning that Clare lays good in her publication.
- Does now not bore with syntax!
- Helps you research the underlying recommendations fascinated with querying a database, and from there the syntax is straightforward
- Provides incredibly transparent examples and causes
- Is academically sound whereas being sensible and approachable
Read or Download Beginning SQL Queries: From Novice to Professional PDF
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Clare Churcher's starting SQL Queries is your advisor to gaining knowledge of the lingua franca of the database undefined: the SQL language. sturdy wisdom of SQL is essential to a person operating with databases, since it is with SQL that you just retrieve information, manage info, and generate company effects. realizing tips on how to write strong queries is the root for all paintings performed in SQL, and it's a starting place that Clare lays good in her publication.
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Extra info for Beginning SQL Queries: From Novice to Professional
Then we want to see only the names, that is, a subset of the columns, so we can use a project operation to retrieve those. Altogether, the algebra looks like the expression in Listing 3-12 and can be implemented by the SQL expression in Listing 3-13. Listing 3-12. Algebra to Retrieve Subset of Information from the View AllTourInfo PLastName, FirstName (SYear=2006 AND Type=‘Open’(AllTourInfo)) Listing 3-13. SQL to Retrieve Subset of Information from the View AllTourInfo SELECT LastName, FirstName FROM AllTourInfo WHERE TourType = 'Open' AND Year = 2006 If we didn’t want to have the intermediate step of creating a view, we could combine all the operations into one SQL query as in Listing 3-14 where the name of the view has been replaced with the SQL SELECT statement, Listing 3-11, that we used to define it.
Say we want to find all the men our club, as in Figure 2-2a. Fortunately, when we designed our database in Chapter 1, we foresaw such a query and included an attribute Gender in the Member table. We want just that subset of rows where the value in the Gender field is “M”, so this becomes the condition for the select operation. Listing 2-1 shows the notation for this operation. The Greek letter sigma (V) is shorthand for select, the table we are applying the operation to is in parentheses (Member), and the subscript Gender = 'M' is the condition.
This means we can apply another operation to the result of the first operation and so build up complex queries. We can use successive operations to create an algebra expression for the query in Figure 2-2c, retrieving the names and handicaps of junior members. First we find the rows for juniors using a select operation, and then we use a project operation to retrieve the required columns from the result. Listing 2-10 shows the full expression. Listing 2-10. Combining a Select and Project Operation SLastName, FirstName, Handicap (VMemberType = 'Junior' (Member)) As you can see, the algebra tells us how to get the result we want.
Beginning SQL Queries: From Novice to Professional by Clare Churcher