Detailed introduction to the syntax and precautions of Oracle stored procedures

A stored procedure is a special program in the Oracle database that can accept parameters, execute a series of SQL statements and branch statements, and ultimately return results or have an impact. Using stored procedures can simplify complex SQL statements and improve database performance and security. So, how to write Oracle stored procedures? The following will introduce the syntax and precautions of Oracle stored procedures in detail.

1. Create a stored procedure

The syntax for creating a stored procedure is as follows:

CREATE [OR REPLACE] PROCEDURE procedure_name
[(parameter1 [IN | OUT | IN OUT ] type1 [, parameter2 [IN | OUT | IN OUT] type2 ...])]
IS
[local_variable_declarations]
BEGIN
executable_statements
[EXCEPTION
exception_handler_statements]
END [procedure_name];

Among them, CREATE indicates the command to create a stored procedure; [OR REPLACE] indicates that if the stored procedure already exists, replace the original stored procedure; PROCEDURE indicates that the stored procedure is created; parameter1, parameter2, etc. represent the input or output parameters of the stored process, there can be multiple, and the parameter type can be any legal data type; IS means that the next part is the main body of the stored process; [local_variable_declarations] means that all the parameters in the stored process can be defined. Required local variables; between BEGIN and END is the execution part of the stored procedure, which can contain any SQL statement, including SELECT, INSERT, UPDATE, DELETE, etc.; if an exception occurs during execution, you can add EXCEPTION and exception_handler_statements to define exception handling statement.

2. Stored procedure parameters

Stored procedures can have input parameters, output parameters and input/output parameters. When creating a stored procedure, you need to define a name and type for each parameter, and specify whether it is an IN, OUT, or IN OUT type. Input parameters are used to pass values ​​to stored procedures, output parameters are used to store the values ​​returned by stored procedures, and input/output parameters can be used as both input parameters and output parameters.

The following is an example of a simple stored procedure parameter definition:

CREATE PROCEDURE test_proc (

p1 IN VARCHAR2,
p2 OUT NUMBER,
p3 IN OUT DATE

) IS
BEGIN

-- 执行业务逻辑

END;

In this example, the stored procedure has three parameters: p1 is an input parameter, type VARCHAR2; p2 is an output parameter, type NUMBER; p3 is an input/output parameter, type DATE.

3. The main body of the stored procedure

The main part of the stored procedure contains execution statements and flow control statements. In the main part, you can use DECLARE to define local variables, you can use SQL statements such as SELECT, INSERT, UPDATE, and DELETE to perform data operations, and you can use process control statements such as IF, CASE, and LOOP to implement business logic.

The following is an example of a simple stored procedure body:

CREATE PROCEDURE test_proc AS

v_count NUMBER;

BEGIN

SELECT COUNT(*) INTO v_count FROM test_table;
IF v_count > 100 THEN
    DELETE FROM test_table;
END IF;

END;

In this example, the main part of the stored procedure uses a SELECT statement to query the number of records in the test_table table, and assigns the result to the v_count variable; uses the IF statement to determine whether the value of v_count is greater than 100, and if it is greater than 100, uses the DELETE statement Delete all records in the test_table table.

4. Exception handling

Exceptions may occur during the execution of a stored procedure, such as primary key conflicts, null pointer references, etc. In order to prevent these exceptions from affecting the normal operation of the program, exception handling statements need to be added to the stored procedure.

Exception handling statements in Oracle stored procedures include operations when an exception occurs, as well as the definition of exception types and exception messages. Stored procedures can use the EXCEPTION statement to define exception handlers and the RAISE statement to throw exceptions.

The following is a simple exception handling example:

CREATE PROCEDURE test_proc AS

v_count NUMBER;

BEGIN

SELECT COUNT(*) INTO v_count FROM non_existent_table;

EXCEPTION

WHEN NO_DATA_FOUND THEN
    DBMS_OUTPUT.PUT_LINE('No data found');
WHEN OTHERS THEN
    DBMS_OUTPUT.PUT_LINE('An error occurred');
    RAISE;

END ;

In this example, the stored procedure attempts to query a non-existent table and will generate a NO_DATA_FOUND exception. An exception handler is added to the stored procedure. When an exception occurs, an exception message is output and the RAISE statement is used to throw the exception to the caller.

5. Summary

Stored procedure is a very important program in Oracle database, which can improve the performance and security of the database, and also makes writing SQL statements easier and more intuitive. When writing a stored procedure, you need to pay attention to the definition of parameters, the writing of the stored procedure body, and the definition of exception handlers. Only by using stored procedures rationally can the Oracle database achieve the highest performance and security.

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