What is the difference between stored procedures and functions in oracle

Difference: 1. Stored procedures are used to complete specific operations or tasks in the database, while functions are used for specific data; 2. The program header of the stored procedure is declared with PROCEDURE, and no return type is required when declaring. The program header of the function is declared with FUNCTION, and the return type must be described when declaring.

The operating environment of this tutorial: Windows 7 system, Oracle 11g version, Dell G3 computer.

Stored Procedure

Stored Procedure (Stored Procedure) is a set of SQL statements to complete specific functions. It is compiled and stored in the database. middle. The user executes a stored procedure by specifying its name and giving parameters (if the stored procedure has parameters). Stored procedures are an important object in the database, and any well-designed database application should use stored procedures. A stored procedure is a procedure written by flow control and SQL statements. This procedure is compiled and optimized and stored in the database server. It only needs to be called when the application program uses it. In ORACLE, several related procedures can be combined together to form a program package.

Advantages:

1. The stored procedure is only compiled when it is created. There is no need to recompile the stored procedure every time it is executed in the future. However, the general SQL statement is compiled every time it is executed. It is compiled once, so using stored procedures can improve database execution speed.

2. When performing complex operations on the database (such as Update, Insert, Query, and Delete on multiple tables), this complex operation can be encapsulated in a stored procedure and combined with the transaction processing provided by the database. use.

3. Stored procedures can be reused, which can reduce the workload of database developers.

4. High security, you can set that only a certain user has the right to use the specified stored process.

The difference between stored procedures and functions

The biggest difference between the two is:

1 ). Functions always return data to the caller, and generally only return a value; 2). Stored procedures (procedures) do not directly return data, but can change the values ​​of output parameters, which can be approximately regarded as returning values. , and there is no limit on the number of values ​​for the stored procedure output parameters.

From a general application point of view, if you do not need a return value or need multiple return values, use a stored procedure. If you only use one return value, use a function.

2. There can only be DDL (such as select, etc.) statements in the function definition; DML statements are mainly included in the procedure (when performing complex operations on the database, such as Update, Insert, Query, and Delete on multiple tables) ).

If you want to use the result set of select, you must use a cursor

Actual example

1. Function

(1) Create function

create or replace function get_salary（
    dept_no number,
    emp_count **out** number)
    return number IS
    v_sum number;begin
    ...exception    ...end get_salary

(2) Call function

declare 
    v_num number;
    v_sum number;begin
    ...（这里应该出现函数名表示调用）end

2, stored procedure

(1) Create stored procedure

create or replace procedure pro_demo(
    dept_no number default 10,
    sal_sum out number,
    emp_count out number)
IS
begin
    ...
exception
    ...
end proc_demo;

(2) Call stored procedure

Calling syntax:

1), exec ;

2), execute ;

3), in PL/SQL Called directly in the statement block.

For example:

declare
    v_num number;
    v_sum number(8,2);
begin
    procedure pro_demo(dept_no=>1,sal_num=>900,emp_count=>10)（这里出现存储过程名表示调用，传递参数值用=>）
end;

3. Local stored procedure

In PL/SQL, you can also create a local stored procedure in the declare block instead of The purpose of using the keyword create is to avoid storing the stored procedure in the database and avoid the trouble caused by changing the database. Its main usage scenario is to temporarily use a stored procedure instead of reusing it many times in the future. .

Example:

declare
    v_num number;
    v_sum number(8,2);
procedure proc_demo(
    dept_no number default 10,
    sal_sum out number,
    emp_count out number)
IS
begin
    ...（这里不用出现存储过程名）
exception
    ...
end proc_demo;

Recommended tutorial: "Oracle Tutorial"

The difference between stored procedures and functions

Stored Procedure	Function
Used to complete specific operations or tasks in the database (such as insertion, deletion, etc.)	Used for specific data ( Such as query return value)
Use PROCEDURE in the program header declaration	Use FUNCTION in the program header declaration
The return type is not required when declaring the program header	The return type must be described when declaring the program header, and PL/SQL The block must include at least one valid RETURN statement
You can use IN/OUT/IN OUT 3 parameter modes	You can use IN/OUT/IN OUT 3 parameter modes
Can be executed as an independent PL/SQL statement	Cannot be executed independently, must be called as part of an expression
Can return zero or more values ​​via OUT/IN OUT	The RETURN statement returns a value, and the value is consistent with the declaration part. You can also bring out variables through OUT type parameters
##SQL statement Stored procedures cannot be called in (DML or SELECT)	Functions can be called in SQL statements (DML or SELECT)

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