It is also the standard language used to access and manipulate data in modern relational and object-relational database systems. In a procedural language program, the execution of most statements depends on previous or subsequent statements and on control structures, such as loops or conditional branches, that are not available in SQL.
The procedural nature of these languages makes them more complex than SQL, but it also makes them more flexible and powerful.
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The combination of both nonprocedural and procedural language elements in an OCI program provides easy access to an Oracle database in a structured programming environment. OCI supports all SQL data definition, data manipulation, query, and transaction control facilities that are available through an Oracle database. For example, an OCI program can run a query against an Oracle database. The query can require the program to supply data to the database using input bind variables, as follows:. In the preceding SQL statement, :empnumber is a placeholder for a value that is to be supplied by the application.
The applications you develop can be more powerful and flexible than applications written in SQL alone. OCI also provides facilities for accessing and manipulating objects in a database. OCI has facilities for working with object types and objects. An object type is a user-defined data structure representing an abstraction of a real-world entity.
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For example, the database might contain a definition of a person object. The object type definition serves as the basis for creating objects that represent instances of the object type by using the object type as a structural definition, you could create a person object with the attribute values 'John', 'Bonivento', and '30'.
Object types may also contain methods —programmatic functions that represent the behavior of that object type. Oracle Database Concepts. These capabilities include:. For a more detailed description, see "Encapsulated Interfaces". Different types of SQL statements require different processing steps in your program. It is important to take this into account when coding your OCI application.
Oracle Database recognizes several types of SQL statements:. Data definition language DDL statements manage schema objects in the database. DDL statements create new tables, drop old tables, and establish other schema objects.
They also control access to schema objects. DDL statements also allow you to work with objects in the Oracle database, as in the following series of statements that create an object table:. OCI applications treat transaction control, session control, and system control statements as if they were DML statements. Data manipulation language DML statements can change data in the database tables. For example, DML statements are used to:. Queries are statements that retrieve data from a database. A query can return zero, one, or many rows of data.
Queries access data in tables, and they are often classified with DML statements. However, OCI applications process queries differently, so they are considered separately in this guide. Queries can require the program to supply data to the database using input bind variables, as in the following example:. When processing a query, an OCI application also must define output variables to receive the returned results.
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In the preceding statement, you must define an output variable to receive any name values returned from the query. Among these are:.
Combine procedural control statements with several SQL statements, so that they are executed as a unit. They represent input values passed to the database when the statement is processed. These placeholders must be bound to C language variables in your program. OCI processes SQL statements as text strings that an application passes to the database on execution. A separate precompilation step is then necessary to generate an executable application. This guide uses special terms to refer to the different parts of a SQL statement.
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For example, consider the following SQL statement:. Two select-list items - customer and address. A table name in the FROM clause - customers. When you develop your OCI application, you call routines that specify to the Oracle database the address location of input and output variables of your program. In this guide, specifying the address of a placeholder variable for data input is called a bind operation. Specifying the address of a variable to receive select-list items is called a define operation.
These terms and operations are described in Chapter 4. All the data structures that are used by OCI calls are encapsulated in the form of opaque interfaces that are called handles. A client allocates certain types of handles, populates one or more of those handles through well-defined interfaces, and sends requests to the server using those handles. In turn, applications can access the specific information contained in a handle by using accessor functions.
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The OCI library manages a hierarchy of handles. Encapsulating the OCI interfaces with these handles has several benefits to the application developer, including:. Reduction of server-side state information that must be retained, thereby reducing server-side memory usage. Improvement of productivity by eliminating the need for global variables, making error reporting easier, and providing consistency in the way OCI variables are accessed and used.
OCI provides application developers with simplified user authentication and password management in several ways:.
OCI enables the application to update a user's password, which is particularly helpful if an expired password message is returned by an authentication attempt. A simplified login function for sessions by which a single user connects to the database using a login name and password.
A mechanism by which a single OCI application authenticates and maintains multiple sessions by separating the login session the session created when a user logs in to an Oracle database from the user sessions all other sessions created by a user. OCI provides several feature extensions to improve application performance and scalability. Application performance has been improved by reducing the number of client to server round-trips required, and scalability improvements have been made by reducing the amount of state information that must be retained on the server side.
Some of these features include:. Implicit prefetching of SELECT statement result sets to eliminate the describe round-trip, reduce round-trips, and reduce memory usage. Improved scalability by providing the ability to concentrate connections, processes, and sessions across users on connections and by eliminating the need for separate sessions to be created for each branch of a global transaction. Allowing applications to authenticate multiple users and allow transactions to be started on their behalf.
OCI provides a comprehensive application programming interface for programmers seeking to use Oracle Database object capabilities. These features can be divided into the following major categories:. Type Management: Mapping and Manipulation Functions to access information about object types and control data attributes of Oracle types. The object cache is a client-side memory buffer that provides lookup and memory management support for objects. It stores and tracks object instances that have been fetched by an OCI application from the server to the client side.
The object cache is created when the OCI environment is initialized. When multiple applications run against the same server, each has its own object cache.
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