Oracle is a very powerful database management system that has many advanced functions and features, of which stored procedures are one of them. A stored procedure is a set of predefined SQL statements for database operations that can be stored in the database for later call use.
In Oracle, stored procedures are written in PL/SQL, a language that combines SQL and programming. PL/SQL has strong data manipulation capabilities and process control capabilities, and can easily write efficient stored procedures.
Benefits of stored procedures
The main benefit of stored procedures is that it can increase the execution efficiency of the database and reduce network communication overhead. Because the stored procedure has been pre-compiled and optimized, there is no need to repeatedly parse and optimize it during execution, and can be directly called for execution. In addition, stored procedures can also implement dynamic operations through parameters, which not only simplifies the code but also avoids risks such as SQL injection.
Creation and execution of stored procedures
The following describes how to create and execute stored procedures in Oracle.
Create a stored procedure
In Oracle, you need to use the CREATE PROCEDURE statement to create a stored procedure. The syntax is as follows:
CREATE [OR REPLACE] PROCEDURE procedure_name [(parameter_name [IN | OUT | IN OUT] parameter_type [, ...])] [IS | AS] BEGIN pl/sql_code_block; END [procedure_name];
Among them:
The following example code demonstrates how to create a simple stored procedure that accepts two parameters and outputs their sum:
CREATE OR REPLACE PROCEDURE add_nums( num1 IN NUMBER, num2 IN NUMBER, sum OUT NUMBER ) IS BEGIN sum := num1 + num2; END add_nums;
Execute the stored procedure
In In Oracle, the EXECUTE or EXECUTE IMMEDIATE statement is required to execute a stored procedure. For example, to execute the above sample program, you can use the following statement:
DECLARE
result NUMBER;
BEGIN
add_nums(10, 20, result);
DBMS_OUTPUT.PUT_LINE('The sum is: ' || result);
END;Here we use the DECLARE statement to declare the variable result that needs to be used, and call the add_nums stored procedure and output the result to the screen.
Parameter type
In a stored procedure, parameters can be input parameters, output parameters or bidirectional parameters.
The method of declaring the parameter type is as follows:
(param_name [IN | OUT | IN OUT] param_type [, ...])
In this declaration, [IN | OUT | IN OUT] is an optional parameter, used to specify the type of the parameter. If the parameter type is not specified, it defaults to the IN type, that is, the input parameter.
Sample code:
CREATE OR REPLACE PROCEDURE my_proc ( num IN NUMBER, str IN OUT VARCHAR2, cur OUT SYS_REFCURSOR ) IS BEGIN -- 逻辑实现 END my_proc;
In the above code, we declare a stored procedure my_proc containing three parameters. The first parameter num is the input parameter, and the second parameter str is bidirectional. Parameters, the third parameter cur is the output parameter.
Record set processing
When using stored procedures to operate data, it is often necessary to return a query result list. Oracle provides two types of recordsets: cursors and PL/SQL tables.
Cursor
A cursor is a data structure that returns a result set, which can traverse query results. Cursors can be explicit or implicit. Explicit cursors require declaring a cursor variable and opening and closing it in code. Implicit cursors are automatically created and managed by Oracle.
Here is a stored procedure that demonstrates how to use a cursor:
CREATE OR REPLACE PROCEDURE get_employee(
id_list IN VARCHAR2,
emp_cur OUT SYS_REFCURSOR
)
IS
BEGIN
OPEN emp_cur FOR 'SELECT * FROM employees WHERE id IN (' || id_list || ')';
END get_employee;In this example, we declare a stored procedure get_employee with two parameters, which accepts a comma-separated list of employees The ID list is used as an input parameter and a cursor emp_cur containing the selected employee information is returned.
PL/SQL table
PL/SQL table is an array-like data structure that can store a set of values. PL/SQL tables have many practical applications in stored procedures, such as passing a set of data to a stored procedure, etc.
In Oracle, PL/SQL tables can be declared and used in stored procedures, such as the following code:
CREATE OR REPLACE PACKAGE my_package IS TYPE num_list IS TABLE OF NUMBER INDEX BY PLS_INTEGER; PROCEDURE sum_nums(nums IN num_list, sum OUT NUMBER); END my_package; CREATE OR REPLACE PACKAGE BODY my_package IS PROCEDURE sum_nums(nums IN num_list, sum OUT NUMBER) IS total NUMBER := 0; BEGIN FOR indx IN 1 .. nums.COUNT LOOP total := total + nums(indx); END LOOP; sum := total; END sum_nums; END my_package;
Here, we create a package named my_package, which declares A PL/SQL table type named num_list and a stored procedure sum_nums that uses that type. sum_nums accepts an argument of type num_list and calculates their sum.
Conclusion
In Oracle, stored procedures are one of the important tools for maintaining databases. They have efficient execution capabilities and dynamics. We can also use stored procedures to let it execute some business logic instead of just executing a single SQL statement, which can improve reusability and maintainability. Because they can be stored in a database and shared and accessed by multiple applications or processes. There are many benefits to using stored procedures, and it is difficult to cover them all in just a short article, but we believe that as long as you have an in-depth understanding and application, you will benefit a lot in actual work.
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