The Language of SQL- P44 ppt

... database, and the best way often relates to the type of software that will be used with the data. Looking Ahead This chapter covered the principles of database design. We went over the basics of the normalization ... period? ■ Are there special analysis requirements for the data? If there is more than one teacher for the same subject, do you want to be able to compare t...

Ngày tải lên: 05/07/2014, 05:20

... that time. Generally speaking, there are three major components of the SQL language. The first is called DML, or Data Manipulation Language. This module of the language allows you to retrieve, ... been The Logic of SQL. This is because, like all computer languages, the language of SQL has much more to do with cold, hard logic than with English vocabulary. Nevertheless,...

Ngày tải lên: 05/07/2014, 05:20

... stored in any number of tables. The term relational is used to indicate that the tables are related to each other. For example, let’s take the simple case of a database consisting of only two tables: ... and the data they contain. The common custom is to display a table as a grid of rows and columns. Each row represents a record in the table. Each column represents a field...

Ngày tải lên: 05/07/2014, 05:20

... statement. The FROM keyword is used to designate the table from which data is to be retrieved. The name of the table follows the FROM. In this case, the table name is Customers. As is the custom, ... such, the principles of database design will be much more meaningful after you’re more aware of the details and nuances of retrieving some data. So we’re going to tempor...

Ngày tải lên: 05/07/2014, 05:20

... define the logic of the CASE expression. The WHEN and THEN keywords define a condition that is evaluated. If the value after the WHEN is true, then the result after THEN is utilized. The WHEN and THEN ... value2 THEN result2 (repeat WHEN-THEN any number of times) [ELSE DefaultResult] END As can be seen, the CASE expression utilizes a number of keywords other than CASE: W...

Ngày tải lên: 05/07/2014, 05:20

... rows where the Quan tityPurchased column has a value of 5. In the real world, the selection of data is often far from straightforward. Accordingly, let’s now turn our attention to ways of specifying ... in the row for William Smith. Therefore, it determines that both the William Smith and the Natalie Lopez rows meet the condition. Obviously, this isn’t what was meant. This...

Ngày tải lên: 05/07/2014, 05:20

... Customers.CustomerID Two blank lines were inserted to clearly separate the subquery from the rest of the statement. The subquery is the middle section of the statement. Using a Subquery as a Data Source 143 chapter ... or view. Notice that the subquery is given a table alias of CashOrders, which allows the columns in the subquery to be referenced in the main SELECT....

Ngày tải lên: 05/07/2014, 05:20

... first SELECT has an original name of OrderDate. The first column of the second SELECT has an original name of ReturnDate. To ensure that the first column in the final result has the desired name, both OrderDate ... only pulls data that is in both of the two sets being looked at. The INTERSECT is analogous to the AND operator and handles the second scenario stated at...

Ngày tải lên: 05/07/2014, 05:20

... statements gives you the possi- bility of much greater flexibility. The term parameter in SQL statements is similar to the term variable, as it is used in other computer languages. A parameter ... ure is executed, the calling program passes a value for the parameter, and the SQL statement is executed as if that value were part of the statement. It should also be noted that...

Ngày tải lên: 05/07/2014, 05:20

... operator D n acts on the n-th variable of u. Proof . The demonstration follows straightforwardly from the theorem on products (Theorem IV.8) using [u]=  n  n [u].  The behavior of the gradient unfortunately ... forecasting, i.e. finding the best estimate of r(h) or P (h, T ),wecan project r(h) and P (h, T ) onto the space of what is known at time zero, either in the...

Ngày tải lên: 24/03/2014, 04:20