MySQL Triggers - Implementation Issue - mysql

Question

I am developing a MySQL database using Workbench. I want two send two fields from a newly created record to another table. I would then like to update the original table with newly created data from the second table. I was looking to implement this with triggers, unless there is a better way of course :) My attempt was a fail when I went to upload it(see below)
Specifically, I would like tc_Event to send the ID & tc_EventTags_ID to tc_EventTags to fill in tc_Tag_ID & tc_Event_ID. Afterwards I want the ID of tc_EventTags sent back to tc_Event to the tc_EventTags_ID field.
Thanks for any help.
-- -----------------------------------------------------
-- Table `mcontest`.`tc_EventTags`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mcontest`.`tc_EventTags` (
`ID` INT NOT NULL AUTO_INCREMENT ,
`tc_Tag_ID` INT NOT NULL ,
`tc_Event_ID` INT NOT NULL ,
PRIMARY KEY (`ID`) ,
INDEX `fk_tc_EventTags_tc_Tag1` (`tc_Tag_ID` ASC) ,
INDEX `fk_tc_EventTags_tc_Event1` (`tc_Event_ID` ASC) ,
CONSTRAINT `fk_tc_EventTags_tc_Tag1`
FOREIGN KEY (`tc_Tag_ID` )
REFERENCES `mcontest`.`tc_Tag` (`ID` )
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_tc_EventTags_tc_Event1`
FOREIGN KEY (`tc_Event_ID` )
REFERENCES `mcontest`.`tc_Event` (`ID` )
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = MyISAM;
-- -----------------------------------------------------
-- Table `mcontest`.`tc_Event`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mcontest`.`tc_Event` (
`ID` INT NOT NULL AUTO_INCREMENT ,
`date` DATE NOT NULL ,
`time` TIME NOT NULL ,
`location` VARCHAR(45) NOT NULL ,
`description` VARCHAR(45) NOT NULL ,
`tc_EventTags_ID` INT NULL ,
`tc_Orgs_ID` INT NOT NULL ,
`tc_PersonEvent_ID` INT NOT NULL ,
PRIMARY KEY (`ID`) ,
INDEX `fk_tc_Event_tc_EventTags1` (`tc_EventTags_ID` ASC) ,
INDEX `fk_tc_Event_tc_Orgs1` (`tc_Orgs_ID` ASC) ,
INDEX `fk_tc_Event_tc_PersonEvent1` (`tc_PersonEvent_ID` ASC) ,
CONSTRAINT `fk_tc_Event_tc_EventTags1`
FOREIGN KEY (`tc_EventTags_ID` )
REFERENCES `mcontest`.`tc_EventTags` (`ID` )
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_tc_Event_tc_Orgs1`
FOREIGN KEY (`tc_Orgs_ID` )
REFERENCES `mcontest`.`tc_Orgs` (`ID` )
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_tc_Event_tc_PersonEvent1`
FOREIGN KEY (`tc_PersonEvent_ID` )
REFERENCES `mcontest`.`tc_PersonEvent` (`ID` )
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = MyISAM;
USE `mcontest`;
DELIMITER $$
USE `mcontest`$$
CREATE TRIGGER eventTag_Trigger
AFTER insert ON tc_Event
FOR EACH ROW BEGIN
INSERT INTO tc_EventTags values('',NEW.tc_Event_ID);
END;
END$$
DELIMITER ;
SET SQL_MODE=#OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=#OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=#OLD_UNIQUE_CHECKS;

Answer 1

Why have put a tc_EventTags_ID in table tc_Event? What is the logic behind that?
I mean that the relationship between the 2 tables would be (I guess): 1 Event - many EventTags. This is already achieved by the tc_EventTags.tc_Event_ID which is a Foreign Key to tc_Event.
To answer your question:
As it is now, the Trigger tries for every row inserted in table Event, to add a row in table EventTag. But it will fail for 2 reasons:
EventTag has 2 Constraints (Foreign keys) which have to be fulfilled for the triggered insert to succeed. So, tc_Event_ID is ok but tc_Tag_ID has to be NOT NULL and reference the Tag table but the value you supply, '', probably is not in table Tag.
EDIT: the value you supply, '', is also a CHAR while it should be INT.
But trigger will probably not be started at all, since every time you insert a row in table Event, those constraints have to be fulfilled and one of them is the tc_EventTags_ID which references EventTag table. But EventTag table is empty. Do you see the circular logic here?