oracle cursor usage

oracle cursor usage: 1. Explicit cursor, use the CURSOR keyword to define the cursor, and then specify the SELECT query statement in the cursor; 2. Implicit cursor, used to execute SQL statements in PL/SQL code; 3. Cursor attributes, used to obtain the current status of the cursor; 4. Cursor variables, used to reference variables of the cursor object, and can be declared and used in PL/SQL blocks; 5. Cursor parameters, parameters of stored procedures or functions. transfer.

Oracle cursor (Cursor) is a database object used to process query result sets in PL/SQL programs. Cursors can be used to process query results row by row, or to return a multi-row result set in a procedure or function. Below I will introduce the usage of Oracle cursors in detail.

1. Use of Explicit Cursor:

Define the cursor: Use the CURSOR keyword to define the cursor, and then specify the SELECT query statement in the cursor.

CURSOR cursor_name IS SELECT column1, column2 FROM table_name WHERE 
condition;

Open the cursor: Use the OPEN statement to open the cursor to execute the query.

OPEN cursor_name;

Retrieve cursor data: Use the FETCH statement to retrieve the data in the cursor row by row.

FETCH cursor_name INTO variable1, variable2;

Close the cursor: After processing the data, use the CLOSE statement to close the cursor.

CLOSE cursor_name;

2. The use of implicit cursor:

Implicit cursor is the default cursor in Oracle database and is used in PL/SQL code Execute SQL statements. Oracle automatically creates and manages implicit cursors when using SELECT, INSERT, UPDATE, or DELETE statements. The following is an example of using an implicit cursor:

SELECT column1, column2 INTO variable1, variable2 FROM table_name WHERE 
condition;

3. Use of cursor attributes:

The cursor object has some built-in attributes that can be used to obtain the current value of the cursor. Status, such as determining whether the cursor is open, the number of rows returned in the result set, etc.

• SQL%ISOPEN: used to determine whether the cursor is open.

• SQL%FOUND: used to determine whether the cursor finds matching data rows.

• SQL%NOTFOUND: Used to determine whether the cursor has not found a matching data row.

• SQL%ROWCOUNT: used to get the number of rows in the cursor.

4. Cursor variables:

Cursor variables are variables used to reference cursor objects, and can be declared in PL/SQL blocks and use. Cursor variables can be passed to subroutines so that different blocks of code can share the same cursor.

cursor_variable_name cursor_name%ROWTYPE;

5. Cursor parameters:

A cursor can be passed as a parameter of a stored procedure or function, so that the cursor results can be accessed when the procedure or function is called. This makes code reuse more convenient and flexible.

6. Cursors are used to process result sets:

Cursors can be used to process query result sets row by row, such as using loop structures and cursors to read data row by row, Perform complex calculations, updates, or delete operations.

7. Cursors are used to return result sets:

Cursors can also be used to return multi-row result sets in stored procedures or functions. You can obtain query results when a procedure or function is called by defining a parameter that returns a cursor. The following is a simple example:

PROCEDURE get_employee_data (p_cursor OUT SYS_REFCURSOR) AS
BEGIN
OPEN p_cursor FOR
SELECT employee_id, employee_name FROM employees;
END;

To sum up, Oracle cursor is an important tool for processing query results in PL/SQL. It can be used to process query result sets row by row, and can also be used to store Return a multi-row result set from a procedure or function. The use of cursors can help us process database query results more flexibly, perform data processing and result return.

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