MySQL Cursors

MySQL Cursors
- Definition
- Syntax
- Example

1. MySQL Cursors
Reggie Niccolo Santos
UP ITDC

2. Outline

What is a cursor?

Additional characteristics

Syntax

Example

3. What is a cursor?

Allows you to iterate through a result set
returned by a SELECT statement

Allows you to iterate over a set of rows
returned by a query and process each row
accordingly

4. MySQL Cursor Characteristics

Read-only
-You cannot update data in the
underlying table through the cursor

5. MySQL Cursor Characteristics

Non-scrollable
-You can only fetch rows in the order
determined by the SELECT
statement
-You cannot fetch rows in the
reversed order
-You cannot skip rows or jump to a
specific row in the result set

6. MySQL Cursor Characteristics

Asensitive
-Points to the actual data, whereas
an insensitive cursor uses a
temporary copy of the data
-Faster than an insensitive cursor

7. Syntax
DECLARE cursor_name CURSOR FOR
select_statement
OPEN cursor_name
FETCH [[NEXT] FROM] cursor_name INTO
var_name [, var_name] ...
CLOSE cursor_name

8. Things to Note

The SELECT statement cannot have an
INTO clause

Cursor declarations must appear before
handler declarations and after variable and
condition declarations

9. Things to Note

If no more rows are available, a No Data
condition occurs with a SQLSTATE value
'02000'. To detect this condition, you can
setup a handler for it (or for a NOT FOUND
condition)

10. Example
DECLARE v_finished INTEGER DEFAULT 0;
DECLARE v_email VARCHAR(255) DEFAULT "";
DECLARE email_list VARCHAR(1000) DEFAULT "";

# declare cursor for student email
DECLARE email_cursor CURSOR FOR
SELECT email FROM
student_record.students;

# declare NOT FOUND handler
DECLARE CONTINUE HANDLER
FOR NOT FOUND SET v_finished = 1;

11. Example
OPEN email_cursor;
get_email: LOOP
FETCH email_cursor INTO v_email;
IF v_finished = 1 THEN
LEAVE get_email;
END IF;
-- build email list
SET email_list = CONCAT(v_email, ";",
email_list);
END LOOP get_email;
CLOSE email_cursor;

12. References

Http://www.mysqltutorial.org/mysql-cursor/

Http://www.brainbell.com/tutorials/MySQL/Working_With_Cursors.htm