I have a table called test like this:
CREATE TABLE test(
id int auto_increment primary key,
prefix varchar(1) not null default ('s'),
newid varchar(10) null);
I would like column newid to be combined values of column id and column prefix when inserting new values into table test. For example:
id prefix newid
1 s s1
2 s s2
...
So i tried to create after insert trigger like this:
DELIMITER $$
CREATE TRIGGER test
AFTER INSERT ON test
for each row BEGIN
set newid = concat(id,prefix);
END$$
DELIMITER ;
But i got this error:
#1193 - Unknown system variable 'newid'
Please tell me what I need to fix to achieve the result needed.
Best Regards
Related
I have a MySQL table created using the following syntax:
CREATE TABLE `name_to_id` (
`id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR(128),
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
);
And a common query this table would like to answer is name to id look-up, but if the <name, id> pair does not exist in the DB, then also insert a new entry and return the newly inserted id.
Can I know should I do that in MySQL?
As commented by Strawberry, this cannot be performed in a single query.
However, here is a stored procedure that should do what you expect. First, it uses the INSERT ... ON DUPLICATE KEYS UPDATE syntax to insert new names ; this actually relies on the UNIQUE key that you correctly set up on the name column.
DELIMITER //
CREATE PROCEDURE get_id_by_name(IN p_name VARCHAR(128))
BEGIN
INSERT INTO name_to_id(name) VALUE(p_name) ON DUPLICATE KEY UPDATE name = p_name;
SELECT id FROM name_to_id WHERE name = p_name;
END //
DELIMITER ;
Demo on DB Fiddle.
This approach is efficient, but the downside of ON DUPLICATE KEYS is that it wastes id sequences : everytime the query is called, the sequence is autoincremented (even if a record already exists). This can be seen in the fiddle.
Here is another approach, that won't burn sequence numbers :
DELIMITER //
CREATE PROCEDURE get_id_by_name(IN p_name VARCHAR(128))
BEGIN
DECLARE p_id bigint(20) unsigned;
SELECT id INTO p_id FROM name_to_id WHERE name = p_name;
IF (p_id IS NULL) THEN
INSERT INTO name_to_id(name) VALUE(p_name);
SELECT LAST_INSERT_ID();
ELSE
SELECT p_id;
END IF;
END //
DELIMITER ;
Demo on DB Fiddle.
you can do this on stored proc, if the select statement did not return a result, then you can execute the insert statement
I created a table
Databases Name - mytrigger;
Table name - employee_audit
use mytrigger;
create table employee_audit(
id int auto_increment primary key,
employeeNumber int not null,
lastName varchar(50) not null,
changee datetime default null,
action varchar(50) default null
);
After that, I created one update trigger
My trigger name is
before_employees_update
DELIMITER $$
create trigger before_employees_update
before update on employee_audit
for each row
begin
insert into employee_audit
set action ='update',
employeeNumber = OLD.employeeNumber,
lastName = OLD.lastName,
changee = now();
end$$
DELIMITER ;
After that, I inserted values in table using this command ->
insert into employee_audit values(1,112,'prakash','2015-11-12 15:36:20' ,' ');
After that, I want to update my table row where id =1
update employee_audit set lastName = 'Sharma' where employeeNumber =112;
But it is not executed give an error
ERROR 1442 (HY000): Can't update table 'employee_audit' in stored
function/trigger because it is already used by statement which invoked
this stored function/trigger.
When I searched on Google I found a lot of Question with the same error. But not able to fix my problem. what is the reason I'm not able to update my row?
What i suggest,you can create one log table like employee_audit_LOG .
And on every insert or update in main table you can make new entry in this table or update existing record.
Also you can add updated_timestamp column to that LOG table which maintain when did specific record get updated.
The error itself tells you the answer. This is because, you can't use the same table on which trigger is being executed. You need to store your audit logs into some different table.
I need a solution for copy the auto increment value to userid column when insert the record.
I have two column like id(AI),userid. Here I have used a trigger
CREATE TRIGGER adduserid BEFORE INSERT ON user
FOR EACH ROW SET NEW.userid = NEW.id
The problems is triggers invoke before insert,so it will get id as 0.
Suggest me how can I modify the trigger?
Sample:
Table definition:
CREATE TABLE departments (
ID NUMBER(10) NOT NULL,
DESCRIPTION VARCHAR2(50) NOT NULL);
ALTER TABLE departments ADD (
CONSTRAINT dept_pk PRIMARY KEY (ID));
CREATE SEQUENCE dept_seq;
Trigger definition:
CREATE OR REPLACE TRIGGER dept_bir
BEFORE INSERT ON departments
FOR EACH ROW
BEGIN
SELECT dept_seq.NEXTVAL
INTO :new.id
FROM dual;
END;
Syntax Link1:https://dev.mysql.com/doc/refman/5.0/en/create-trigger.html
I have the following table.
CREATE TABLE people(
first_name VARCHAR(128) NOT NULL,
nick_name VARCHAR(128) NULL
)
I would like to prevent people from having their nickname be the same as their firstname if they attempt that insertion. I do not want to create an index on either of the columns just a rule to prevent the insertion of records where the first_name and nick_name are the same.
Is there a way to create a rule to prevent insertion of records where the first_name would equal the nick_name?
CREATE TRIGGER `nicknameCheck` BEFORE INSERT ON `people` FOR EACH ROW begin
IF (new.first_name = new.nick_name) THEN
SET new.nick_name = null;
END IF;
END
Or you can set first_name to NULL which will cause SQL error and you can handle it and show some warning.
You only need triggers for BEFORE INSERT and BEFORE UPDATE. Let these check the values and abort the operation, if they are equal.
Caveat: On older but still widely used versions of MySQL (before 5.5 IIRC) you need to do something bad, such as read from the written table or easier read from an inexistant table/column (in order to abort).
AFTER INSERT trigger to test and remove if same ...
CREATE TABLE ek_test (
id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
one INT NOT NULL,
two INT NOT NULL
);
delimiter //
CREATE TRIGGER ek_test_one_two_differ AFTER INSERT ON ek_test
FOR EACH ROW
BEGIN
IF (new.one = new.two) THEN
DELETE FROM ek_test WHERE id = new.id;
END IF;
END//
delimiter ;
INSERT INTO ek_test (one, two) VALUES (1, 1);
SELECT * FROM ek_test;
NOTE you will also need AFTER UPDATE trigger.
I think in PostgreSQL you can use a function to generate your primary key in a table instead of just using auto_increment. Something similar to:
CREATE TABLE `blah` (
`id` bigint(20) unsigned NOT NULL my_generator_function(),
etc.
Where my_generator_function() would return a bigint.
Is that possible with MySQL or do I have to do that from the application code myself?
You can create a trigger -
CREATE TRIGGER trigger1
BEFORE INSERT
ON table1
FOR EACH ROW
BEGIN
IF NEW.id = 0 THEN -- generate new ID if zero is set
SET NEW.id = ...; -- write your code to generate new ID
END IF;
END