Throw an error in a MySQL trigger

Throw an error in a MySQL trigger

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If I have a trigger before the update on a table, how can I throw an error that prevents the update on that table?


Here is one hack that may work. It isn't clean, but it looks like it might work:

Essentially, you just try to update a column that doesn't exist.

How can we use SIGNAL statement with MySQL triggers?, i need a trigger to give an error message if invalid data is inserted.here is my trial and its not working. please help on error handling in mysql. DELIMITER $$ -- before inserting new id DROP TRIGGER IF EXISTS before_insert_id$$ CREATE TRIGGER before_insert_id BEFORE INSERT ON test FOR EACH ROW BEGIN -- condition to check IF NEW.id < 0 THEN -- hack to solve absence of SIGNAL/prepared statements in triggers UPDATE `Error: invalid_id_test` SET x=1; END IF; END$$ DELIMITER ;


As of MySQL 5.5, you can use the SIGNAL syntax to throw an exception:

signal sqlstate '45000' set message_text = 'My Error Message';

State 45000 is a generic state representing "unhandled user-defined exception".


Here is a more complete example of the approach:

delimiter //
use test//
create table trigger_test
(
    id int not null
)//
drop trigger if exists trg_trigger_test_ins //
create trigger trg_trigger_test_ins before insert on trigger_test
for each row
begin
    declare msg varchar(128);
    if new.id < 0 then
        set msg = concat('MyTriggerError: Trying to insert a negative value in trigger_test: ', cast(new.id as char));
        signal sqlstate '45000' set message_text = msg;
    end if;
end
//

delimiter ;
-- run the following as seperate statements:
insert into trigger_test values (1), (-1), (2); -- everything fails as one row is bad
select * from trigger_test;
insert into trigger_test values (1); -- succeeds as expected
insert into trigger_test values (-1); -- fails as expected
select * from trigger_test;

trigger Throw error message, So we can do the validation in an IF statement inside the trigger, but how can we cancel the insert/update and throw an error? MySQL 5.5  MySQLTutorial.org is a website dedicated to MySQL database. We regularly publish useful MySQL tutorials to help web developers and database administrators learn MySQL faster and more effectively. All MySQL tutorials are practical and easy-to-follow, with SQL script and screenshots available. More About Us


Unfortunately, the answer provided by @RuiDC does not work in MySQL versions prior to 5.5 because there is no implementation of SIGNAL for stored procedures.

The solution I've found is to simulate a signal throwing a table_name doesn't exist error, pushing a customized error message into the table_name.

The hack could be implemented using triggers or using a stored procedure. I describe both options below following the example used by @RuiDC.

Using triggers
DELIMITER $$
-- before inserting new id
DROP TRIGGER IF EXISTS before_insert_id$$
CREATE TRIGGER before_insert_id
    BEFORE INSERT ON test FOR EACH ROW
    BEGIN
        -- condition to check
        IF NEW.id < 0 THEN
            -- hack to solve absence of SIGNAL/prepared statements in triggers
            UPDATE `Error: invalid_id_test` SET x=1;
        END IF;
    END$$

DELIMITER ;
Using a stored procedure

Stored procedures allows you to use dynamic sql, which makes possible the encapsulation of the error generation functionality in one procedure. The counterpoint is that we should control the applications insert/update methods, so they use only our stored procedure (not granting direct privileges to INSERT/UPDATE).

DELIMITER $$
-- my_signal procedure
CREATE PROCEDURE `my_signal`(in_errortext VARCHAR(255))
BEGIN
    SET @sql=CONCAT('UPDATE `', in_errortext, '` SET x=1');
    PREPARE my_signal_stmt FROM @sql;
    EXECUTE my_signal_stmt;
    DEALLOCATE PREPARE my_signal_stmt;
END$$

CREATE PROCEDURE insert_test(p_id INT)
BEGIN
    IF NEW.id < 0 THEN
         CALL my_signal('Error: invalid_id_test; Id must be a positive integer');
    ELSE
        INSERT INTO test (id) VALUES (p_id);
    END IF;
END$$
DELIMITER ;

Validating data with triggers in MySQL · Cvuorinen.net, Here is the syntax of creating a MySQL BEFORE UPDATE trigger: value is 3 times greater than old value, then raise an error by using the SIGNAL statement:. MySQLTutorial.org is a website dedicated to MySQL database. We regularly publish useful MySQL tutorials to help web developers and database administrators learn MySQL faster and more effectively. All MySQL tutorials are practical and easy-to-follow, with SQL script and screenshots available. More About Us


The following procedure is (on mysql5) a way to throw custom errors , and log them at the same time:

create table mysql_error_generator(error_field varchar(64) unique) engine INNODB;
DELIMITER $$
CREATE PROCEDURE throwCustomError(IN errorText VARCHAR(44))
BEGIN
    DECLARE errorWithDate varchar(64);
    select concat("[",DATE_FORMAT(now(),"%Y%m%d %T"),"] ", errorText) into errorWithDate;
    INSERT IGNORE INTO mysql_error_generator(error_field) VALUES (errorWithDate);
    INSERT INTO mysql_error_generator(error_field) VALUES (errorWithDate);
END;
$$
DELIMITER ;


call throwCustomError("Custom error message with log support.");

MySQL BEFORE UPDATE Trigger By Practical Examples, to use MySQL SIGNAL and RESIGNAL statements to raise error conditions from a stored program e.g., stored procedure, stored function, trigger or event. END IF; END$$ DELIMITER ; DELIMITER $$ DROP TRIGGER IF EXISTS before_tblinvoice_delete $$ CREATE TRIGGER before_tblinvoice_delete BEFORE DELETE ON tblinvoice FOR EACH ROW BEGIN IF (SELECT COUNT(*) FROM tblinvoicedetails WHERE tblinvoicedetails.idtblinvoice = old.idtblinvoice) > 0 THEN SET NEW='Error: Cannot delete this item.


CREATE TRIGGER sample_trigger_msg 
    BEFORE INSERT
FOR EACH ROW
    BEGIN
IF(NEW.important_value) < (1*2) THEN
    DECLARE dummy INT;
    SELECT 
           Enter your Message Here!!!
 INTO dummy 
        FROM mytable
      WHERE mytable.id=new.id
END IF;
END;

Raising Error Conditions with SIGNAL / RESIGNAL , — AFTER INSERT and AFTER UPDATE on the blog table. A simple trick is to call a non existing stored procedure to trigger a MySQL error. If you use some generic name for the non existing procedure, like throw_error(), you will not be getting a very useful error message so it can be quite confusing especially for people that do not know about this trigger and the constraint it enforces. This can be improved a little bit by using the error message in the actual call, so the error message becomes a little bit more relevant.


Is it possible to modify an existing trigger definition in MySQL , Also learn tools to create MySQL Triggers, Example on AFTER INSERT, assignment of expression results to variables, and error handling. At the SQL level, the output from SHOW WARNINGS and SHOW ERRORS indicates the MYSQL_ERRNO and MESSAGE_TEXT values in the Code and Message columns. To retrieve information from the diagnostics area, use the GET DIAGNOSTICS statement (see Section 13.6.7.3, “GET DIAGNOSTICS Statement” ).


How to Create Database Triggers in MySQL, Causing MySQL to raise an exception from a trigger. gistfile1.sql. -- MySQL does not implement raising exceptions within triggers. Here's a hacky model for  Recently I got this question twice. Although SIGNAL was implemented in version 6.0 (which is partially mysql-trunk now) this version is not stable yet, so users still need to use workaround.


MySQL 8.0 Reference Manual :: 24.3.1 Trigger Syntax and , I am new to MySQL and I'm having problems creating a BEFORE INSERT trigger. I get an unexpected END error. I have a table named verlof_aanvragen with a  If the THROW statement is specified without parameters, it must appear inside a CATCH block. This causes the caught exception to be raised. Any error that occurs in a THROW statement causes the statement batch to be terminated. % is a reserved character in the message text of a THROW statement and must be escaped.