Trigger MySql while using CONCAT inserting data is Null - mysql

Question

This is the query i execute after insertation in some table in my database. Here i am getting rate_like_id and all other fields i also save them but when i use CONCAT and trying to save them as json it inserts NULL value via trigger.
Is this a wrong way to do this. Is ther any other way i can save this type of data via trigger mysql.
INSERT INTO `log_activity`(`visitor_id`,
`rating_like_id`,
`type`,
`response`,
`created_by`,
`created_date`)
VALUES (new.created_by,
new.rating_like_id,
CASE WHEN new.is_like = NULL THEN "Rating" ELSE "Like" END ,
-- Here is this column Should not be null but it is coming null when INSERTED
CONCAT(
'{"card_id":','"',new.card_id,'"',
',"card_type":','"',new.card_type,'"',
',"user_id":','"',new.user_id,'"',
',"is_like":','"',new.is_like,'"',
',"has_rated":','"',new.has_rated,'"',
',"rate":','"',new.rate,'"',
',"created_by":','"',new.created_by,'"',
',"created_date":','"',new.created_date,'"',
',"card_type":','"',new.card_type,'"','}'),
new.created_by,
new.created_date)
what is wrong with this .. all other fields are saved correctly only CONCAT field is not getting inserted properly.
Yes I am able to insert value like this
CONCAT(" hi "," how "," are "," you ", " ? ")
Is this problem because i am using "new.fieldName" inside CONCAT ... i see THIS question they are doing the same thing .. ofcource it is less complex compare to mine.

Answer 1

If you see comments and conversation between me and marcB.. you will get the answer...
Here i want to show what changes i made to my query to make it work.
marcB said :- Remember that sql null is contagious. if ANY of the fields you're concatting are themselves null, the ENTIRE result becomes null
so you can see my query in question.. i do not have checked for any value is it null or not. So i just had to add the null check.
INSERT INTO `log_activity`(`visitor_id`,
`rating_like_id`,
`type`,
`response`,
`created_by`,
`created_date`)
VALUES (new.created_by,
new.rating_like_id,
CASE WHEN new.is_like = NULL THEN "Rating" ELSE "Like" END,
CONCAT('{"card_id":',
'"',
IFNULL(new.card_id, ''),
'"',
',"card_type":',
'"',
IFNULL(new.card_type, ''),
'"',
',"user_id":',
'"',
IFNULL(new.user_id, ''),
'"',
',"is_like":',
'"',
IFNULL(new.is_like, ''),
'"',
',"has_rated":',
'"',
IFNULL(new.has_rated, ''),
'"',
',"rate":',
'"',
IFNULL(new.rate, ''),
'"',
',"created_by":',
'"',
IFNULL(new.created_by, ''),
'"',
',"created_date":',
'"',
IFNULL(new.created_date, ''),
'"',
',"card_type":',
'"',
IFNULL(new.card_type, ''),
'"',
'}'),
new.created_by,
new.created_date)
It checks for the null value of the field.