每次使用触发器插入 MySQL 5.6 中的目标表后，尝试将 Last updated row_id 从源表拉到另一个表

Question

Hi I have two tables Experiment and Sample. I want to create a trigger such that whenever I insert a row into Sample table it should pull the recent 'Experiment_id' that is generated by MySQL in the 'Experiment' table and pull into a column of 'Sample' table named 'Experiment_id'.

EXPERIMENT TABLE
Experiment_id(auto_incremented)  Exp_name
1                                  abc

SAMPLE TABLE
Sample_id   Experiment_id sample_name
1              1                    
2              1           
3              1                    
4              1           
5              1           
6              1

**New Entry Exp name - xyz**

EXPERIMENT TABLE
Experiment_id(auto_incremented)  Exp_name
1                                  abc
2                                  xyz

SAMPLE TABLE
Sample_id   Experiment_id sample_name
1              1                    
2              1           
3              1                    
4              1           
5              1           
6              1
7              2           
8              2          
9              2                    
10             2 

So Sample id '1-6' is generated when there is only 'Experiment_id' 1 is existing in the 'Experiment' table and Sample_ id '7-10' is generated when experiment_id 2 is auto generated by MySQL.

I am using mysql 5.6. Please someone help me, thanks!!

Answer 1

You will have to use both trigger to track insert and update:

 DROP TRIGGER IF EXISTS trigger_experiment_after_insert;
  DELIMITER $$

  CREATE  TRIGGER trigger_experiment_after_insert
  AFTER INSERT ON experiment FOR EACH ROW
  BEGIN
    -- sample_id will be auto_increment
    INSERT INTO sample_log SET experiment_id = NEW.experiment_id;
  END; $$

  DELIMITER ;

Use update trigger to track update:

 DROP TRIGGER IF EXISTS trigger_experiment_after_update;
  DELIMITER $$

  CREATE  TRIGGER trigger_experiment_after_update
  AFTER UPDATE ON experiment FOR EACH ROW
  BEGIN
    -- sample_id will be auto_increment
    INSERT INTO sample_log SET experiment_id = OLD.experiment_id;
  END; $$

  DELIMITER ;

Answer 2

I wouldn't use a trigger for that. Just use a subquery in the INSERT statement:

INSERT INTO SAMPLE (sample_name, Experiment_id) VALUES (
  'sample name',
  (SELECT MAX(Experiment_id) FROM EXPERIMENT)
)

If you want to do it with a trigger, try this:

create trigger SAMPLE_before_insert before insert on SAMPLE FOR EACH ROW 
  set new.Experiment_id = (select max(Experiment_id) from EXPERIMENT);