I'm trying to write a query for my final year project that would allow me to identify whether students prefer modules in a university degree with less exam weighting. I got help from someone and he suggested that I could use MySQL stored procedures to do that query.
Here is what I got so far:
DELIMITER //
CREATE PROCEDURE ModuleExamWeight()
BEGIN
DECLARE EnrollmentCount INT Default 0;
--DECLARE Outputresult varchar(255) DEFAULT "";
--DECLARE output1 INT Default 0;
--DECLARE output2 INT Default 0;
DECLARE finished INT DEFAULT 0;
DECLARE Clist varchar(255) DEFAULT "";
DECLARE c1 CURSOR FOR SELECT MODULEID FROM Modules ORDER BY Examweight;
-- declare NOT FOUND handler
DECLARE CONTINUE HANDLER
FOR NOT FOUND SET finished = 1;
-- open module cursor
OPEN c1;
-- loop through module cursor by getting the number of enrollments per module
MODULES_LIST : LOOP
FETCH c1 INTO Clist;
SELECT ModuleID, COUNT(StudentID) INTO EnrollmentCount FROM ModuleEnrollment;
IF finished = 1 THEN
LEAVE MODULES_LIST;
END IF;
END LOOP MODULES_LIST;
CLOSE c1;
-- This is like my first idea which doesn't work in order to print out the results.
-- SELECT ModuleID, ExamWeight, #EnrollmentCount FROM ModuleEnrollment;
END //
DELIMITER ;
Basically I want to print out the result of this query such as this:
Display ModuleID for each module
Display Exam Weighting for them
Display the values of the enrollment count variable for them.
However, I do not know how do that in a MySQL stored procedure.It would be nice if someone could help me on that. Thank you. I hope my question makes sense.
Related
I was hoping to get some help the the below question, unfortunately the script I have created isn't working. Any assistance would be greatly appreciated!
Question:
Write a script that creates a stored procedure named test. This stored procedure should create a cursor for a result set that consists of the product_name and list_price columns for each product with a list price that’s greater than $700. The rows in this result set should be sorted in descending sequence by list price. The stored procedure should accept an OUT parameter where a message is passed out of the procedure. Then, the procedure should set the out parameter to a string variable that includes the product_name and list price for each product so it looks something like this:
Gibson SG,2517.00|Gibson Les Paul,1199.00|
Here, each value is enclosed in asterisk(*), each column is separated by a comma (,) and each row is separated by a pipe character (|).
My script:
CREATE PROCEDURE test( OUT message VARCHAR(200) )
BEGIN
DECLARE product_name_var VARCHAR(50);
DECLARE list_price_var DECIMAL(9,2);
DECLARE row_not_found TINYINT DEFAULT FALSE;
DECLARE s_var VARCHAR(400) DEFAULT '';
DECLARE invoice_cursor CURSOR for
SELECT
product_name,
list_price
FROM
products
WHERE
list_price > 700
ORDER BY list_price DESC;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET row_not_found = TRUE;
OPEN invoice_cursor;
FETCH invoice_cursor INTO product_name_var, list_price_var;
WHILE row_not_found = FALSE DO
SET s_var = CONCAT(s_var,'*', product_name_var,'*,*',list_price_var,'*|');
FETCH invoice_cursor INTO product_name_var, list_price_var;
END WHILE;
SELECT s_var AS message;
END
SELECT s_var AS message; - message is seen as an alias
use
SET MESSAGE = s_var ;
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=c43887fd68a17e5b1dc2093d10cd03ec
and beware nulls...
Im just trying using stored procedure in mysql. i tried to create a table name "Book". i have 5 columns before. they are idBook, bookName, bookYear, and Stock. So, i added 2 columns for rating and review. and i wanted to give those column with value using looping in stored procedure. and this is my code :
DELIMITER $$
CREATE DEFINER=`root`#`localhost` PROCEDURE `getBookExcitement`()
BEGIN
DECLARE bookRating INT DEFAULT 0;
DECLARE count INT DEFAULT 0;
DECLARE bookReview VARCHAR (100);
DECLARE sums INT;
SELECT count(idBook) INTO sums FROM Book;
getBookExcitement : LOOP
SET count = count+1;
IF count<sums then
SELECT FLOOR(1 + (rand()*5)) INTO bookRating;
IF bookRating <3 then
SET bookReview = 'This book isn't good';
ELSEIF bookRating <=4 OR bookRating >=3 then
SET bookReview = 'This book is good';
ELSE
SET bookReview = 'This book is very good, you should read it';
END IF;
UPDATE Book SET Rating = bookRating AND Review = bookReview
WHERE idBuku=count;
END IF;
END LOOP getBookExcitement;
END
but when i try to call it, my workbench just keep executing the query non stop. Just like it stuck in loop. but the way i see it, i cant find something wrong with that looping, please help me since im new with stored procedure in mysql.
thanks
There's no LEAVE getBookExcitement;
Put an else at the end of the IF count<sums then block, with a LEAVE statement.
I am in the process of converting a SQL Server 2005 database to MySQL and having problems with a Stored procedure. I'm new to MySQL stored procedures so I'm sure it is a problem with my conversion but I'm not seeing it.
The stored procedure is supposed to generate a temporary table which is used to populate a Data Grid View in a vb.net application. However, I'm getting the error "Data No Data - Zero rows fetched, selected or processed.". Seems simple enough but the select procedure in the stored procedure will get data if I just run it as a query which is why I don't understand why the error.
I'm really hoping someone can tell me why because I have several hundred stored procedures to convert and I'm having this problem on the very first one.
Here's the Stored Procedure:
DELIMITER $$
DROP PROCEDURE IF EXISTS `usp_get_unassigned_media`$$
CREATE DEFINER=`showxx`#`67.111.11.110` PROCEDURE `usp_get_unassigned_media`()
BEGIN
/* GET CURSOR WITH LOCAL LOCATIONS */
DECLARE intKey INT;
DECLARE dteDateInserted DATETIME;
DECLARE vchIdField VARCHAR(200);
DECLARE vchValueField VARCHAR(200);
DECLARE intLastKey INT;
/*TAKE OUT SPECIFIC PLAYLIST ITEMS IF TOO SLOW*/
DECLARE csrMediaToBeAssigned CURSOR FOR
SELECT
`media`.`key` AS `key`,
`media`.`date_inserted` AS `date_inserted`,
`media_detail_types`.`id` AS `id`,
`media_details`.`value` AS `value`
FROM (`media`
LEFT JOIN (`media_detail_types`
JOIN `media_details`
ON ((`media_detail_types`.`key` = `media_details`.`detail_key`)))
ON ((`media_details`.`media_key` = `media`.`key`)))
WHERE ((`media`.`is_assigned` = 0)
AND ((`media_detail_types`.`id` = 'Volume Name')
OR (`media_detail_types`.`id` = 'Drive Id')))
ORDER BY `media`.`key`,`media`.`date_inserted`,`media_detail_types`.`id`;
OPEN csrMediaToBeAssigned;
DROP TEMPORARY TABLE IF EXISTS temp_unassigned_media;
CREATE TEMPORARY TABLE temp_unnassigned_media
(temp_key INT, DateInserted DATETIME, IdField VARCHAR(200), ValueField VARCHAR (200))
ENGINE=MEMORY;
SET intLastKey = 0;
/*--GET FIRST RECORD */
FETCH FROM csrMediaToBeAssigned
INTO intKey, dteDateInserted, vchIdField, vchValueField;
/*--LOOP THROUGH CURSOR */
WHILE intLastKey = 0 DO
/*--DATA SHOULD BE IN DRIVE ID THEN VOLUME NAME */
INSERT INTO temp_unnassigned_media
VALUES (intKey, dteDateInserted, vchValueField, '');
FETCH NEXT FROM csrMediaToBeAssigned
INTO intKey, dteDateInserted, vchIdField, vchValueField;
UPDATE temp_unnassigned_media
SET IdField = vchValueField
WHERE temp_key = temp_key;
FETCH NEXT FROM csrMediaToBeAssigned
INTO intKey, dteDateInserted, vchIdField, vchValueField;
END WHILE;
SELECT *
FROM temp_unnassigned_media
ORDER BY date_inserted;
CLOSE csrMediaToBeAssigned;
/*DEALLOCATE csrMediaToBeAssigned */
/*DROP TABLE #temp_unnassigned_media */
END$$
DELIMITER ;
You never hit a condition where that WHILE loop will exit; you initialize intLastKey variable, but it never changes, so you fetch through the entire resultset. The exception is thrown when you fetch again, after the last record.
The normative pattern is to declare a CONTINUE HANDLER, which MySQL will execute when the NOT FOUND condition is triggered. The handler is normally used to set a variable, which you can then test, so you know when to exit the loop.
In your case, it looks like just adding this line, after your DECLARE CURSOR statement and before the OPEN statement, would be sufficient:
DECLARE CONTINUE HANDLER FOR NOT FOUND SET intLastKey = 1;
I've been Googleing around for a while and I am sure that the problem is that I don't understand clearly how CURSORs in MySQL work.
A short explanation of the problem: I'm writing such function (simplified):
CREATE DEFINER=`me`#`localhost` FUNCTION `product_move`(prID INT, tr_type VARCHAR(2), clID INT, am INT, dnID INT, usrID INT, price FLOAT(10,2), ti DATETIME, barc TINYTEXT, cmt TINYTEXT, lnID INT)
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE cur_id INT;
DECLARE net_pr FLOAT(10,2);
DECLARE cur_r INT;
DECLARE remaind INT DEFAULT 0;
DECLARE avg_price FLOAT(10,2) DEFAULT 0;
DECLARE curs CURSOR FOR SELECT `products_transactionsID`,
`price`,
`remains`
FROM `products_transactions`
WHERE `productID`=prID AND `remains`>0 AND `type`='V'
ORDER BY `products_transactionsID` ASC;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN curs;
SET remaind=am;
read_loop:LOOP
FETCH curs INTO cur_id,net_pr,cur_r;
IF done THEN
LEAVE read_loop;
END IF;
IF (cur_r>=remaind) THEN
SET avg_price = avg_price + (net_pr * remaind);
UPDATE `products_transactions` SET `remains`=`remains`-remaind WHERE products_transactionsID=cur_id;
LEAVE read_loop;
ELSE
SET avg_price = avg_price + (net_pr * cur_r);
SET remaind=remaind-cur_r;
UPDATE `products_transactions` SET `remains`=0 WHERE products_transactionsID=cur_id;
END IF;
END LOOP;
CLOSE curs;
SET avg_price=avg_price/am;
INSERT INTO products_transactions
(`products_transactionsID`,`clientID`,`date_created`,`delivery_notesID`,`type`,`productID`,`amountIN`,`amountOUT`,`barcodes`,`in_stock`,`out_stock`,`out_repair`,`out_loss`,`booked`,`ordered`,`userID`,`price`,`comments`,`fifo_buy_price`)
SELECT NULL, clID, ti, dnID , tr_type, prID, 0, am, barc, products_transactions.in_stock-am, products_transactions.out_stock,
products_transactions.out_repair, products_transactions.out_loss, products_transactions.booked, products_transactions.ordered,usrID,price,cmt,avg_price
FROM
products_transactions WHERE productID=prID ORDER BY products_transactionsID DESC LIMIT 1;
So, we insert a new row in this table, based upon some calculations from the previously selected rows and updating these rows meanwhile.
The problem is with the avg_price variable, which should be calculated based on the net_pr variable which is FETCH'ed from the cursor. But somehow, instead of being FETCH'ed from the SELECT, the net_pr variable takes the value of the price input parameter of my function! How is that possible?
My guesses have been so far:
a variable name conflict? Searched through the code but I can't find any.
updating the table within the LOOP could make the CURSOR loose its position? It would make sense, but that wouldn't result in this, either...
I'd apreciate any ideas.
Two things that I can see:
1) Don't update the table that you're using in the cursor. MySQL says the cursor is read only but I wouldn't trust this. Set your value, exit the cursor, and then update the table.
2) Using the same name for a variable in the proc definition and a column in a select gives a conflict: http://dev.mysql.com/doc/refman/5.0/en/local-variable-scope.html
"A local variable should not have the same name as a table column. If an SQL statement, such as a SELECT ... INTO statement, contains a reference to a column and a declared local variable with the same name, MySQL currently interprets the reference as the name of a variable. "
In MySQL, I am converting a table from a single row per item type (a quantity of items) to a single row per item, so that additional detail can be stored about individual items.
Here is an example source table:
id parent_id qty item_type
-- --------- --- ---------
1 10291 2 widget
2 10292 4 thinger
I want to create a new table with a new column containing info that cannot be applied to more than one item. Thus, the above table would end up as follows:
id parent_id item_type info
-- --------- --------- ----
1 10291 widget [NULL]
2 10291 widget [NULL]
3 10292 thinger [NULL]
4 10292 thinger [NULL]
5 10292 thinger [NULL]
6 10292 thinger [NULL]
Is there a way I can iterate or loop each row of the source table, inserting a number of records equal to the source qty column? I would prefer to do this in sql instead of code to keep all of the conversion steps together (there are many others).
You can do with stored procedure. That will be like below. Below is stored procedure I am using for inserting products into log based on their quantity.
Seem you have to do similar task. You can get how to use database cursor in stored procedure to loop over a result set in MySQL from below example.
DELIMITER $$
DROP PROCEDURE IF EXISTS CursorProc$$
CREATE PROCEDURE CursorProc()
BEGIN
DECLARE no_more_products, quantity_in_stock INT DEFAULT 0;
DECLARE prd_code VARCHAR(255);
DECLARE cur_product CURSOR FOR
SELECT productCode FROM products;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET no_more_products = 1;
/* for loggging information */
CREATE TABLE infologs (
Id int(11) NOT NULL AUTO_INCREMENT,
Msg varchar(255) NOT NULL,
PRIMARY KEY (Id)
);
OPEN cur_product;
FETCH cur_product INTO prd_code;
REPEAT
SELECT quantityInStock INTO quantity_in_stock
FROM products
WHERE productCode = prd_code;
IF quantity_in_stock < 100 THEN
INSERT INTO infologs(msg)
VALUES (prd_code);
END IF;
FETCH cur_product INTO prd_code;
UNTIL no_more_products = 1
END REPEAT;
CLOSE cur_product;
SELECT * FROM infologs;
DROP TABLE infologs;
END$$
DELIMITER;
Seems your task is 90% same as above procedure. Just do needful changes. It will work.
I think you can create stored procedure, declare a cursor that reads source table and for each row inserts qty rows into destination table.
Based on other answers which provided some insight, I was able to find additional information (by Kevin Bedell) to create a stored procedure and use a cursor in a loop. I have simplified my solution so that it matches the example in my question:
DROP PROCEDURE IF EXISTS proc_item_import;
DELIMITER $$
CREATE PROCEDURE proc_item_import()
BEGIN
# Declare variables to read records from the cursor
DECLARE parent_id_val INT(10) UNSIGNED;
DECLARE item_type_val INT(10) UNSIGNED;
DECLARE quantity_val INT(3);
# Declare variables for cursor and loop control
DECLARE no_more_rows BOOLEAN;
DECLARE item_qty INT DEFAULT 0;
# Declare the cursor
DECLARE item_cur CURSOR FOR
SELECT
i.parent_id, i.qty, i.item_type
FROM items i;
# Declare handlers for exceptions
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET no_more_rows = TRUE;
# Open the cursor and loop through results
OPEN item_cur;
input_loop: LOOP
FETCH item_cur
INTO parent_id_val, item_type_val, quantity_val;
# Break out of the loop if there were no records or all have been processed
IF no_more_rows THEN
CLOSE item_cur;
LEAVE input_loop;
END IF;
SET item_qty = 0;
qty_loop: LOOP
INSERT INTO items_new
(parent_id, item_type)
SELECT
parent_id_val, item_type_val;
SET item_qty = item_qty + 1;
IF item_qty >= quantity_val THEN
LEAVE qty_loop;
END IF;
END LOOP qty_loop;
END LOOP input_loop;
END$$
DELIMITER ;
Before asking this question, I had not used a stored procedures, cursors, or loops. That said, I have read and encountered them frequently on SE and elsewhere, and this was a good opportunity to learn
It may be worth noting that the example on Kevin's page (linked above) does not use END%% (just END) which caused some headache in trying to get the script to work. When creating a procedure, it is necessary to change the delimiter temporarily so that semicolons terminate statements inside the procedure, but not the creation process of the procedure itself.
That is just an example of code that I have here, it is not adapted to your needs, but it does exactly what you need, and it is simple than a procedure, or temporary table.
SELECT event, id, order_ref, storeitem_barcode_create(8), NOW()
FROM (
SELECT mss.id, mss.event, mss.order_ref, mss.quantity, mss.product_id,
#rowID := IF(#lastProductID = mss.product_id AND #lastID = mss.id, #rowID + 1, 0) AS rowID,
#lastProductID := mss.product_id,
#lastID := mss.id
FROM module_barcode_generator mbg,
(SELECT #rowID := 0, #lastProductID := 0, #lastID := 0) t
INNER JOIN module_events_store_sold mss ON mss.order_ref = "L18T2P"
) tbl
WHERE rowId < quantity;
Typo in JYelton's solution for his/her own question:
FETCH item_cur
INTO parent_id_val, item_type_val, quantity_val;
Should be:
FETCH item_cur
INTO parent_id_val, quantity_val, item_type_val;
Otherwise very good.