Thus, using a simple example pattern: Firebird's implementation does not accord with the SQL standards, which require that a stable set be established before any data are changed.Versions of Firebird from V.3 onward will comply with the standard.
One is to loop through a recordset and update a single row in a table based on a single row lookup in another table.
DELIMITER // DROP PROCEDURE IF EXISTS sp_set_name // CREATE PROCEDURE sp_set_name () BEGIN DECLARE done INT DEFAULT 0; DECLARE client_id INT; DECLARE cur1 CURSOR FOR SELECT id from clients WHERE name IS NULL; DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1; OPEN cur1; read_loop: LOOP IF done THEN LEAVE read_loop; END IF; FETCH cur1 INTO client_id; UPDATE clients SET name = (SELECT name from orders WHERE id = client_id) WHERE id = client_id; END LOOP; close cur1; END; // DELIMITER ; DELIMITER // DROP PROCEDURE IF EXISTS build_phone_list // CREATE PROCEDURE build_phone_list (INOUT phone_list varchar(4000)) BEGIN DECLARE finished INTEGER DEFAULT 0; DECLARE phone varchar(15) DEFAULT ""; DECl ARE phone_cursor CURSOR FOR SELECT phone FROM contacts; DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1; OPEN phone_cursor; phone_loop: LOOP FETCH phone_cursor INTO phone; IF finished = 1 THEN LEAVE phone_loop; END IF; SET phone_list = CONCAT(phone,",",phone_list); END LOOP phone_loop; CLOSE phone_cursor; END; // DELIMITER ; You can test the build_phone_list stored procedure using the following code: SET @phone_list = ""; CALL build_phone_list(@phone_list); SELECT @phone_list; Changes made to the database after the cursor is opened are visible in the result table.
END LOOP cursor_loop; CLOSE cursor1; SET done=0; As a best practice, you should always reset your status variable to 0 after the cursor loop terminates; otherwise, subsequent or nested cursor loops may terminate prematurely.
There are many tasks well suited to cursors, but there are some common uses.
clause, the assignment phrases, containing the columns with the values to be set, are separated by commas.
In an assignment phrase, column names are on the left and the values or expressions containing the assignment values are on the right. A column name can be used in expressions on the right.The string literal is preceded by the character set name, prefixed with an underscore character: ”, will continuously update rows, over and over, and give the impression that the server has hung.Quirks like this can affect any data-changing DML operations, most often when the selection conditions involve a subquery.Cursor declarations must appear after variable and condition declarations but before handler declarations.Also keep in mind that the cursor SELECT statement cannot have an INTO clause; it's strictly read-only.The old value of the column will always be used in these right-side values, even if the column was already assigned a new value earlier in the It was not always like that.