MySQL - Cursor FETCH Statement

Quiz

A cursor in database is a construct which allows you to iterate/traversal the records of a table. In MySQL you can use cursors with in a stored program such as procedures, functions etc.

In other words, you can iterate though the records of a table from a MySQL stored program using the cursors. The cursors provided by MySQL are embedded cursors. They are −

READ ONLY − Using these cursors you cannot update any table.
Non-Scrollable − Using these cursors you can retrieve records from a table in one direction i.e., from top to bottom.
Asensitive − These cursors are insensitive to the changes that are made in the table i.e. the modifications done in the table are not reflected in the cursor.

Which means if we have created a cursor holding all the records in a table and, meanwhile if we add some more records to the table, these recent changes will not be reflected in the cursor we previously obtained.

While Declaring cursors in a stored program you need to make sure these (cursor declarations) always follow the variable and condition declarations.

To use a cursor, you need to follow the steps given below (in the same order)

Declare the cursor using the DECLARE Statement.
Declare variables and conditions.
Open the declared cursor using the OPEN Statement.
Retrieve the desired records from a table using the FETCH Statement.
Finally close the cursor using the CLOSEstatement.

The FETCH statement

The FETCH statement retrieves the next record from the result set of the SELECT statement associated with the DECLARE statement of the cursor. You need to provide the variables list into which the values of the retrieved record are intended to be stored. While doing so, you need to make sure that the number of variables submitted to the FETCH statement are equal to the number of rows retrieved by the SELECT statement.

Syntax

Following is the syntax of the MySQL Cursor FETCH Statement −

FETCH cursor_name INTO variables list;

Example

Assume we have created a table with name Players in MySQL database using CREATE statement as shown below −

CREATE TABLE Players(
   ID INT,
   First_Name VARCHAR(255),
   Last_Name VARCHAR(255),
   Date_Of_Birth date,
   Place_Of_Birth VARCHAR(255),
   Country VARCHAR(255),
   PRIMARY KEY (ID)
);

Now, we will insert 7 records in Players table using INSERT statements −

Insert into Players values
(1, 'Shikhar', 'Dhawan', DATE('1981-12-05'), 'Delhi', 'India'),
(2, 'Jonathan', 'Trott', DATE('1981-04-22'), 'CapeTown', 'SouthAfrica'),
(3, 'Kumara', 'Sangakkara', DATE('1977-10-27'), 'Matale', 'Srilanka'),
(4, 'Virat', 'Kohli', DATE('1988-11-05'), 'Delhi', 'India'),
(5, 'Rohit', 'Sharma', DATE('1987-04-30'), 'Nagpur', 'India'),
(6, 'Ravindra', 'Jadeja', DATE('1988-12-06'), 'Nagpur', 'India'),
(7, 'James', 'Anderson', DATE('1982-06-30'), 'Burnley', 'England');

Following query creates a procedure which reads multiple values from a cursor −

Delimiter //
CREATE PROCEDURE demo()
BEGIN
   DECLARE done INT DEFAULT 0;
   DECLARE playerID INT DEFAULT 0;
   DECLARE firstName VARCHAR(255) DEFAULT "";
   DECLARE lastName VARCHAR(255) DEFAULT "";
   DECLARE DOB DATE;
   DECLARE placeOfBirth VARCHAR(255) DEFAULT "";
   DECLARE playerCountry VARCHAR(255) DEFAULT "";
   DECLARE cur CURSOR FOR
   SELECT ID, First_Name, Last_Name, Date_Of_Birth, 
   Place_Of_Birth, Country FROM Players;
   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
   OPEN cur;
   label:LOOP
   FETCH cur INTO playerID, firstName, lastName, DOB, 
   placeOfBirth, playerCountry;
   IF done = 1 THEN LEAVE label;
   END IF;
   SELECT CONCAT(playerID,' ', firstName,' ', lastName, ' ', DOB, ' ', 
   placeOfBirth, ' ', playerCountry) AS PlayerData;
   END LOOP label;
   CLOSE cur;
END//

You can call the above create procedure as follows −

CALL demo\G;

Output

Following is the output of the above query −

********** 1. row **********
PlayerData: 1 Shikhar Dhawan 1981-12-05 Delhi India
1 row in set (0.00 sec)

********** 1. row **********
PlayerData: 2 Jonathan Trott 1981-04-22 CapeTown SouthAfrica
1 row in set (0.00 sec)

********** 1. row **********
PlayerData: 3 Kumara Sangakkara 1977-10-27 Matale Srilanka
1 row in set (0.01 sec)

********** 1. row **********
PlayerData: 4 Virat Kohli 1988-11-05 Delhi India
1 row in set (0.01 sec)

********** 1. row **********
PlayerData: 5 Rohit Sharma 1987-04-30 Nagpur India
1 row in set (0.01 sec)

********** 1. row **********
PlayerData: 6 Ravindra Jadeja 1988-12-06 Nagpur India
1 row in set (0.01 sec)

********** 1. row **********
PlayerData: 7 James Anderson 1982-06-30 Burnley England
1 row in set (0.01 sec)

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