标签：handlers nes creation compile cap string gen nbsp you
PL/SQL provides a server-side, stored procedural language that is easy-to-use, seamless with SQL, robust, portable, and secure. You can access and manipulate database data using procedural schema objects called PL/SQL program units.
PL/SQL program units generally are categorized as follows:
A subprogram is a PL/SQL block that is stored in the database and can be called by name from an application. When you create a subprogram, the database parses the subprogram and stores its parsed representation in the database. You can declare a subprogram as a procedure or a function.
An anonymous block is a PL/SQL block that appears in your application and is not named or stored in the database. In many applications, PL/SQL blocks can appear wherever SQL statements can appear.
The PL/SQL compiler and interpreter are embedded in Oracle SQL Developer, giving developers a consistent and leveraged development model on both client and server. Also, PL/SQL stored procedures can be called from several database clients, such as Pro*C, JDBC, ODBC, or OCI, and from Oracle Reports and Oracle Forms.
definer‘s rights procedure OR invoker‘s rights procedure
在定义PL/SQL子程序时，指定 authid definer / current user。
如果是definer，是说以定义者的权限执行子程序，这样其他用户即使没有对子程序内部使用的对象有相关权限，也是可以执行子程序。
如果是current user，顾名思义是以当前执行该子程序的用户具有的权限来执行，如果没有子程序内部关联对象的相应权限，则无法执行该子程序。
Oracle Database includes many supplied packages that extend database functionality and provide PL/SQL access to SQL features. For example, the UTL_HTTP package enables HTTP callouts from PL/SQL and SQL to access data on the Internet or to call Oracle Web Server Cartridges. You can use the supplied packages when creating applications or as a source of ideas when creating your own stored procedures.
You can create specifications and reference public procedures without actually creating the package body.
The methods of package definition enable you to specify which variables, cursors, and procedures are public and private. Public means that it is directly accessible to the user of a package. Private means that it is hidden from the user of a package.
You create a package in two parts: the specification and the body. The package specification declares all public constructs of the package, whereas the body defines all constructs (public and private) of the package.
An anonymous block consists of an optional declarative part, an executable part, and one or more optional exception handlers.
Oracle Database compiles the PL/SQL block and places it in the shared pool of the SGA, but it does not store the source code or compiled version in the database for reuse beyond the current instance. Unlike triggers, an anonymous block is compiled each time it is loaded into memory. Shared SQL allows anonymous PL/SQL blocks in the shared pool to be reused and shared until they are flushed out of the shared pool.
PL/SQL blocks can include a variety of different PL/SQL language constructs. These constructs including the following:
Variables and constants
You can declare these constructs within a procedure, function, or package. You can use a variable or constant in a SQL or PL/SQL statement to capture or provide a value when one is needed.
Cursors
You can declare a cursor explicitly within a procedure, function, or package to facilitate record-oriented processing of Oracle Database data. The PL/SQL engine can also declare cursors implicitly.
Exceptions
PL/SQL lets you explicitly handle internal and user-defined error conditions, called exceptions, that arise during processing of PL/SQL code.
PL/SQL can run dynamic SQL statements whose complete text is not known until run time. Dynamic SQL statements are stored in character strings that are entered into, or built by, the program at run time. This technique enables you to create general purpose procedures. For example, you can create a procedure that operates on a table whose name is not known until run time.
Many programming techniques use collection types such as arrays, bags, lists, nested tables, sets, and trees. To support these techniques in database applications, PL/SQL provides the data types TABLE and VARRAY, which enable you to declare associative arrays, nested tables, and variable-size arrays.
A collection is an ordered group of elements, all of the same type. Each element has a unique subscript that determines its position in the collection. To create a collection, you first define a collection type, and then declare a variable of that type.
Collections work like the arrays found in most third-generation programming languages. Also, collections can be passed as parameters. So, you can use them to move columns of data into and out of database tables or between client-side applications and stored subprograms.
A record is a composite variable that can store data values of different types, similar to a struct type in C, C++, or Java. Records are useful for holding data from table rows, or certain columns from table rows.
Suppose you have data about an employee such as name, salary, and hire date. These items are dissimilar in type but logically related. A record containing a field for each item lets you treat the data as a logical unit.
You can use the %ROWTYPE attribute to declare a record that represents a table row or row fetched from a cursor. With user-defined records, you can declare your own fields.
PL/SQL supports both native execution and interpreted execution. In interpreted execution, PL/SQL source code is compiled into a so-called bytecode representation, which is run by a portable virtual computer implemented as part of Oracle Database. In native execution, which offers the best performance on computationally intensive program units, the source code of PL/SQL program units is compiled directly to object code for the given platform. This object code is linked into Oracle Database.
标签：handlers nes creation compile cap string gen nbsp you
原文地址：http://www.cnblogs.com/shulin-peng/p/7798275.html
