I am using Below code to add a first day of the month column to the table with an expression to update automatically. But it's throwing a syntax error. someone pls do help.
ALTER TABLE `abc`.`t1`
ADD COLUMN `First_Day` DATE NULL DEFAULT select DATE_ADD(DATE_ADD(LAST_DAY(report_date),
INTERVAL 1 DAY),
INTERVAL - 1 MONTH) AFTER `Totals`;
mysql won't allow to use expressions for setting default values.
you can create trigger for this purpose.
delimiter $$
CREATE TRIGGER test_trigger BEFORE INSERT ON `product`
FOR EACH ROW SET
NEW.myCol= DATE_ADD(DATE_ADD(LAST_DAY(new.report_date),
INTERVAL 1 DAY),
INTERVAL - 1 MONTH);
END$$
delimiter;
I would question why you would wish to store this but if you must a generated column might do.
drop table if exists t;
create table t(id int, report_date date);
ALTER TABLE t
ADD COLUMN `First_Day` DATE as
(date_add(date_add(last_day(date(report_date)),interval 1 day),interval -1 month));
insert into t (id,report_date) values
(1,'2018-01-08'),(2,'2018-02-09');
select * from t;
+------+-------------+------------+
| id | report_date | First_Day |
+------+-------------+------------+
| 1 | 2018-01-08 | 2018-01-01 |
| 2 | 2018-02-09 | 2018-02-01 |
+------+-------------+------------+
2 rows in set (0.00 sec)
I you choose to go this way or via a trigger you will have to write a one off update to populate this column for existing data.
I have 2 tables (in MySQL):
sales(sale_id, customer_id, sale_date, dicount, stock_item_id, seller_id, quantity)
record example:
a0018 | m9795 | 2017-10-2020 | 5 | MarFT | 0 | B-77028
stock(stock_item_id,supplier_name,supplier_email,supplier_phone,item_category item_name,wholesale_price,markup_price,items_in_stock)
record example:
B-77001 |BSN |direct#bsn.com | 1877333665 | Gainers | True Mass | 2.6kg | 33.75 |44.99 | 500
I need to create a trigger that will add a new record into sales table (recording a new sale, that will autoincrement). At the same time I want stock table to update 'items_in_stock' value (that should decrease by whatver quantity was just sold when there is match on stock_item_id)? I hope this makes sense. I'd appreciate any help. Thanks.
Use this:
DELIMITER $$
CREATE
TRIGGER `OnSalesInsert` BEFORE INSERT ON `Sales`
FOR EACH ROW BEGIN
UPDATE Stock
SET items_in_stock = items_in_stock - new.quantity
WHERE stock_item_id = new.stock_item_id;
END;
$$
DELIMITER ;
I'm working with MySQL through phpMyAdmin. I need to reset the ID fields in one of the tables in my database, but I need to do it based on the publication date of each row. I've been looking everywhere and I can't seem to find a solution :(
The following lines of code work fine, but do not do exactly what I require based on the datetime column:
SET #count = 0;
UPDATE `table_name` SET `table_name`.`ID` = #count:= #count + 1;
So this is what I have:
+----+---------------------+
| ID | post_date |
+----+---------------------+
| 1 | 2013-11-04 20:06:28 |
| 2 | 2012-03-30 11:20:22 |
| 3 | 2014-06-26 22:59:51 |
+----+---------------------+
And this is what I need:
+----+---------------------+
| ID | post_date |
+----+---------------------+
| 1 | 2005-08-02 16:51:48 |
| 2 | 2005-08-02 16:59:36 |
| 3 | 2005-08-02 17:01:54 |
+----+---------------------+
Thanks in advance, guys :)
Try this, a simple approach though.
But you will lose all the relations to other tables since you are
resetting the PRIMARY ID Keys.
# Copy entire table to a temporary one based on the publication date
CREATE TEMPORARY TABLE IF NOT EXISTS `#temp_table` AS SELECT * FROM `wp_posts` ORDER BY `post_date`;
# Drop `ID` column from the temporary table
ALTER TABLE `#temp_table` DROP COLUMN `ID`;
# Reset the table `wp_posts` as well as its `ID`
TRUNCATE TABLE `wp_posts`;
# Exclude `ID` column in the INSERT statement below
INSERT INTO `wp_posts`(`post_author`, `post_date`, ..., `comment_count`) SELECT * FROM `#temp_table`;
# Remove the temporary table
DROP TABLE `#temp_table`;
Also see the ERD for WP3.0 below,
Ref: https://codex.wordpress.org/Database_Description/3.3
Try doing it with the following script. It selects every row of your table and orders the rows by its date ascending. Then your Update-Command will be executed within a loop.
Add the type of the ID of your table to the DECLARE-Statement and change the
field-Name in the UPDATE-Statement to your ID-Column name.
BEGIN
DECLARE col_id BIGINT;
DECLARE stepLoopDone BOOLEAN DEFAULT FALSE;
DECLARE counter INT DEFAULT 1;
DECLARE ORDER_CURSOR CURSOR FOR
SELECT id
FROM wp_posts
ORDER BY post_date ASC;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET stepLoopDone = TRUE;
OPEN ORDER_CURSOR;
myLoop: LOOP
FETCH ORDER_CURSOR INTO col_id;
IF stepLoopDone THEN
LEAVE myLoop;
END IF;
/*YOUR UPDATE COMMAND*/
UPDATE wp_posts
SET id = counter
WHERE id = col_id;
/*YOUR UPDATE COMMAND*/
SET counter = counter + 1;
END LOOP;
CLOSE ORDER_CURSOR;
END
Is it possible to do something like this with mysql?
Imagine I've update query, that runs every time user gives successful answer. Now I'd like to count updates and give +1 bonus point every fourth time...
I could just count rows and divide them by 4, but that would give me non spendable bonus points, because for every update it will get recalculated...
Is there any mysql solution to my problem?
I think you may use trigger and calculate additional bonuses when user gives successful answer.
Here is working example:
DROP TABLE IF EXISTS answer;
CREATE TABLE answer
(
id int not null auto_increment,
bonus int not null,
primary key(id)
);
DELIMITER //
CREATE TRIGGER lucky_trigger BEFORE INSERT ON answer
FOR EACH ROW BEGIN
IF MOD((SELECT AUTO_INCREMENT FROM information_schema.TABLES WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'answer'), 4) = 0 THEN
SET NEW.bonus = NEW.bonus + 1;
END IF;
END //
DELIMITER ;
INSERT INTO answer(bonus) VALUES(1);
INSERT INTO answer(bonus) VALUES(1);
INSERT INTO answer(bonus) VALUES(1);
INSERT INTO answer(bonus) VALUES(1);
SELECT id, bonus FROM answer;
Will give you next output:
+----+-------+
| id | bonus |
+----+-------+
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
+----+-------+
4 rows in set (0.00 sec)
Is there any possibility to use an "after update" trigger only in the case the data has been REALLY changed.
I know of "NEW and OLD". But when using them I'm only able to compare columns.
For example "NEW.count <> OLD.count".
But I want something like: run trigger if "NEW <> OLD"
An Example:
create table foo (a INT, b INT);
create table bar (a INT, b INT);
INSERT INTO foo VALUES(1,1);
INSERT INTO foo VALUES(2,2);
INSERT INTO foo VALUES(3,3);
CREATE TRIGGER ins_sum
AFTER UPDATE ON foo
FOR EACH ROW
INSERT INTO bar VALUES(NEW.a, NEW.b);
UPDATE foo SET b = 3 WHERE a=3;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0
select * from bar;
+------+------+
| a | b |
+------+------+
| 3 | 3 |
+------+------+
The point is, there was an update, but nothing has changed.
But the trigger ran anyway. IMHO there should be a way it doesn't.
I know that I could have used
IF NOW.b <> OLD.b
for this example.
BUT imagine a large table with changing columns.
You have to compare every column and if the database changes you have to adjust the trigger.
AND it doesn't "feel" good to compare every column of the row hardcoded :)
Addition
As you can see on the line
Rows matched: 1 Changed: 0 Warnings: 0
MySQL knows that the line didn't change. But it doesn't share this knowledge with the trigger.
A trigger like "AFTER REAL UPDATE" or something like this would be cool.
As a workaround, you could use the timestamp (old and new) for checking though, that one is not updated when there are no changes to the row. (Possibly that is the source for confusion? Because that one is also called 'on update' but is not executed when no change occurs)
Changes within one second will then not execute that part of the trigger, but in some cases that could be fine (like when you have an application that rejects fast changes anyway.)
For example, rather than
IF NEW.a <> OLD.a or NEW.b <> OLD.b /* etc, all the way to NEW.z <> OLD.z */
THEN
INSERT INTO bar (a, b) VALUES(NEW.a, NEW.b) ;
END IF
you could use
IF NEW.ts <> OLD.ts
THEN
INSERT INTO bar (a, b) VALUES(NEW.a, NEW.b) ;
END IF
Then you don't have to change your trigger every time you update the scheme (the issue you mentioned in the question.)
EDIT: Added full example
create table foo (a INT, b INT, ts TIMESTAMP);
create table bar (a INT, b INT);
INSERT INTO foo (a,b) VALUES(1,1);
INSERT INTO foo (a,b) VALUES(2,2);
INSERT INTO foo (a,b) VALUES(3,3);
DELIMITER ///
CREATE TRIGGER ins_sum AFTER UPDATE ON foo
FOR EACH ROW
BEGIN
IF NEW.ts <> OLD.ts THEN
INSERT INTO bar (a, b) VALUES(NEW.a, NEW.b);
END IF;
END;
///
DELIMITER ;
select * from foo;
+------+------+---------------------+
| a | b | ts |
+------+------+---------------------+
| 1 | 1 | 2011-06-14 09:29:46 |
| 2 | 2 | 2011-06-14 09:29:46 |
| 3 | 3 | 2011-06-14 09:29:46 |
+------+------+---------------------+
3 rows in set (0.00 sec)
-- UPDATE without change
UPDATE foo SET b = 3 WHERE a = 3;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0
-- the timestamo didnt change
select * from foo WHERE a = 3;
+------+------+---------------------+
| a | b | ts |
+------+------+---------------------+
| 3 | 3 | 2011-06-14 09:29:46 |
+------+------+---------------------+
1 rows in set (0.00 sec)
-- the trigger didn't run
select * from bar;
Empty set (0.00 sec)
-- UPDATE with change
UPDATE foo SET b = 4 WHERE a=3;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
-- the timestamp changed
select * from foo;
+------+------+---------------------+
| a | b | ts |
+------+------+---------------------+
| 1 | 1 | 2011-06-14 09:29:46 |
| 2 | 2 | 2011-06-14 09:29:46 |
| 3 | 4 | 2011-06-14 09:34:59 |
+------+------+---------------------+
3 rows in set (0.00 sec)
-- and the trigger ran
select * from bar;
+------+------+---------------------+
| a | b | ts |
+------+------+---------------------+
| 3 | 4 | 2011-06-14 09:34:59 |
+------+------+---------------------+
1 row in set (0.00 sec)
It is working because of mysql's behavior on handling timestamps.
The time stamp is only updated if a change occured in the updates.
Documentation is here:
https://dev.mysql.com/doc/refman/5.7/en/timestamp-initialization.html
desc foo;
+-------+-----------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------+------+-----+-------------------+-----------------------------+
| a | int(11) | YES | | NULL | |
| b | int(11) | YES | | NULL | |
| ts | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------+-----------+------+-----+-------------------+-----------------------------+
BUT imagine a large table with changing columns. You have to compare every column and if the database changes you have to adjust the trigger. AND it doesn't "feel" good to compare every row hardcoded :)
Yeah, but that's the way to proceed.
As a side note, it's also good practice to pre-emptively check before updating:
UPDATE foo SET b = 3 WHERE a=3 and b <> 3;
In your example this would make it update (and thus overwrite) two rows instead of three.
I cant comment, so just beware, that if your column supports NULL values, OLD.x<>NEW.x isnt enough, because
SELECT IF(1<>NULL,1,0)
returns 0 as same as
NULL<>NULL 1<>NULL 0<>NULL 'AAA'<>NULL
So it will not track changes FROM and TO NULL
The correct way in this scenario is
((OLD.x IS NULL AND NEW.x IS NOT NULL) OR (OLD.x IS NOT NULL AND NEW.x IS NULL) OR (OLD.x<>NEW.x))
You can do this by comparing each field using the NULL-safe equals operator <=> and then negating the result using NOT.
The complete trigger would become:
DROP TRIGGER IF EXISTS `my_trigger_name`;
DELIMITER $$
CREATE TRIGGER `my_trigger_name` AFTER UPDATE ON `my_table_name` FOR EACH ROW
BEGIN
/*Add any fields you want to compare here*/
IF !(OLD.a <=> NEW.a AND OLD.b <=> NEW.b) THEN
INSERT INTO `my_other_table` (
`a`,
`b`
) VALUES (
NEW.`a`,
NEW.`b`
);
END IF;
END;$$
DELIMITER ;
(Based on a different answer of mine.)
In here if there any row affect with new insertion Then it will update on different table in the database.
DELIMITER $$
CREATE TRIGGER "give trigger name" AFTER INSERT ON "table name"
FOR EACH ROW
BEGIN
INSERT INTO "give table name you want to add the new insertion on previously given table" (id,name,age) VALUES (10,"sumith",24);
END;
$$
DELIMITER ;
Use the following query to see which rows have changes:
(select * from inserted) except (select * from deleted)
The results of this query should consist of all the new records that are different from the old ones.
MYSQL TRIGGER BEFORE UPDATE IF OLD.a<>NEW.b
USE `pdvsa_ent_aycg`;
DELIMITER $$
CREATE TRIGGER `cisterna_BUPD` BEFORE UPDATE ON `cisterna` FOR EACH ROW
BEGIN
IF OLD.id_cisterna_estado<>NEW.id_cisterna_estado OR OLD.observacion_cisterna_estado<>NEW.observacion_cisterna_estado OR OLD.fecha_cisterna_estado<>NEW.fecha_cisterna_estado
THEN
INSERT INTO cisterna_estado_modificaciones(nro_cisterna_estado, id_cisterna_estado, observacion_cisterna_estado, fecha_cisterna_estado) values (NULL, OLD.id_cisterna_estado, OLD.observacion_cisterna_estado, OLD.fecha_cisterna_estado);
END IF;
END
Here are two interesting dead ends (as of MySQL 5.7)-
The new.* and old.* constructs are invalid, MySQL complains about Unknown table 'new' or syntax to use near '*, which precludes tricks like
select ... from (select (select new.* union select old.*)a having count(*)=2) has_change
The documentation for "ROW_COUNT()" has a useful clue-
For UPDATE statements, the affected-rows value by default is the number of rows actually changed
And indeed, after an update statement, ROW_COUNT() correctly shows the count of rows that had changes from the update. However, during the update, inside the trigger, ROW_COUNT() = 0 always. That function has no useful value in a row-level trigger, and there's no statement-level trigger in MySQL as of this answer.
Hope this "null result" prevents future frustration.