How to use cursors to write stored procedures in Oracle

Oracle is a widely used relational database management system. It provides a function called stored procedures that supports the use of cursors to manage data. A stored procedure can be thought of as a pre-compiled block of SQL code that accepts parameters, performs a series of database operations, and returns results. This article will introduce how to use cursors to write stored procedures in Oracle.

1. Overview of Cursors and Stored Procedures

A cursor is a pointer that can be used to traverse the query result set and return the data therein. In Oracle, cursors can be used for stored procedures and functions. A stored procedure is a precompiled program that can be stored in a database and called when needed. Stored procedures have the following benefits:

1. Improved performance

Stored procedures only need to be compiled once, instead of compiling SQL statements every time they are executed. This can greatly improve database performance.

2. Can reduce network overhead

Stored procedures are usually executed on the database server, which means that the transmission of data from the server to the client can be reduced, thereby reducing network overhead.

3. Multiple use

Because stored procedures can be stored in the database, they can be used repeatedly and called in multiple applications.

2. Basic usage of cursor

A cursor is a pointer variable that contains a result set of one or more records. In Oracle, you can use cursors to traverse a result set and perform processing on the data within it. The basic usage of cursors is as follows:

1. Declaring a cursor

A cursor is a PL/SQL object and needs to be declared using the DECLARE statement. Cursor types include explicit and implicit cursors. The following is the format for declaring an explicit cursor:

CURSOR cursor_name IS select_statement;

where cursor_name is the name of the cursor, and select_statement is a SQL statement used to define the result set to be accessed by the cursor. For example, the following is an example of declaring a cursor:

DECLARE
cursor_name CURSOR FOR
SELECT column_name_1, column_name_2
FROM table_name;

2. Open Cursor

Before using the cursor, you need to open it using the OPEN statement. The following is the format for opening a cursor:

OPEN cursor_name;

For example, the following is an example of opening a cursor:

OPEN cursor_name;

3. Reading the cursor

After opening the cursor, you can use the FETCH statement to read data from the cursor. The FETCH statement moves the cursor pointer to the next record and stores the data in the specified variable. The following is the format of the FETCH statement:

FETCH cursor_name INTO variable_name1, variable_name2, ...;

For example, the following is an example of using the FETCH statement to read cursor data:

FETCH cursor_name INTO column1, column2;

4. Close the cursor

After using the cursor, you need to use the CLOSE statement to close it. The following is the format of closing a cursor:

CLOSE cursor_name;

For example, the following is an example of closing a cursor:

CLOSE cursor_name;

3. Use Writing stored procedures with cursors

In Oracle, you can use cursors to write stored procedures. The following are some basic steps about using cursors to write stored procedures:

1. Declaring stored procedures

Use the CREATE PROCEDURE statement to declare a stored procedure and specify the name of the stored procedure and the SQL statements contained in the stored procedure.

The following is an example of declaring a stored procedure:

CREATE PROCEDURE procedure_name
AS
CURSOR cursor_name IS
SELECT column_name_1, column_name_2
FROM table_name;
BEGIN
...
END;

2. Open the cursor

In the stored procedure, you need to use the OPEN statement to open the cursor. The following is an example of opening a cursor:

OPEN cursor_name;

3. Read cursor data and perform other operations

In stored procedures, you need to use FETCH Statements read data from the cursor and perform other operations, such as inserting or updating data. The following is an example of using a cursor to read data and insert new data:

DECLARE
cursor_name CURSOR FOR
SELECT column_name_1, column_name_2
FROM table_name;

variable_name_1 column_name_1%TYPE ;
variable_name_2 column_name_2%TYPE;
BEGIN
OPEN cursor_name;
LOOP

  FETCH cursor_name INTO variable_name_1, variable_name_2;
  EXIT WHEN cursor_name%NOTFOUND;

  INSERT INTO new_table_name
  (column_name_1, column_name_2)
  VALUES (variable_name_1, variable_name_2);

END LOOP;
CLOSE cursor_name;
END;

4. Close the cursor

After the execution of the stored procedure is completed, you need to use the CLOSE statement to close the cursor. The following is an example of closing a cursor:

CLOSE cursor_name;

4. Summary

A cursor is a pointer variable used to traverse a result set and perform processing on the data in it. . In Oracle, you can use cursors to write stored procedures, improve database performance, and reduce network overhead. Stored procedures can be used multiple times and called in multiple applications, which is a very important database feature. In order to use cursors and stored procedures effectively, their usage needs to be carefully studied and practiced appropriately.

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