How to copy data from 1 table to another with different structure - mysql

Question

I have a table with the structure
CREATE TABLE `old_reminder` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`applicant_id` int(11) NOT NULL,
`date` datetime NOT NULL,
`type` enum('payment_15_min','payment_1_day','payment_3_day') NOT NULL DEFAULT 'payment_15_min',
PRIMARY KEY (`id`)
)
and I want to migrate its data to another table with the structure
CREATE TABLE `new_reminders` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`payment_reminder_1_count` int(11) DEFAULT NULL,
`payment_reminder_1_date` datetime DEFAULT NULL,
PRIMARY KEY (`id`)
)
basically multiple rows for each user_id will be converted into 1 row with all the enum values as columns.
I have tried the following but it is updating only 1 row
UPDATE reminders
INNER JOIN old_reminder AS `old`
ON user_id = old.applicant_id
SET new_reminder_1_date = IF(old.type = 'payment_15_min' OR old.type = 'payment_1_day' OR old.type = 'payment_3_day', old.date, '2018-01-01 00:00:00'),
payment_reminder_1_count = IF(old.type = 'payment_15_min' OR old.type = 'payment_1_day' OR old.type = 'payment_3_day',
CASE
WHEN old.type = 'payment_15_min' THEN 1
WHEN old.type = 'payment_1_day' THEN payment_reminder_1_count + 1
WHEN old.type = 'payment_3_day' THEN payment_reminder_1_count + 1 END, 0)
WHERE applicant_id = 123;

Answer 1

If you model looks like this
truncate table old_reminder;
insert into old_reminder (applicant_id,date,type) values (123,'2018-01-01','payment_15_min');
insert into old_reminder (applicant_id,date,type) values (123,'2018-01-02','payment_1_day');
truncate table new_reminders;
insert into new_reminders(user_id,payment_reminder_1_date) values (123,'2016-01-01');
Then a simplified version of your query
update new_reminders n join (select * from old_reminder order by applicant_id,`date`) old on old.applicant_id = n.user_id
SET
enumstr = old.type,
payment_reminder_1_date =
case
when old.type in ('payment_15_min','payment_1_day','payment_3_day') then old.date
else '2017-01-01'
end
WHERE applicant_id = 123;
Produces this result which I think is what you mean by it is updating only 1 row
+----+---------+--------------------------+-------------------------+----------------+
| id | user_id | payment_reminder_1_count | payment_reminder_1_date | enumstr |
+----+---------+--------------------------+-------------------------+----------------+
| 1 | 123 | NULL | 2018-01-01 00:00:00 | payment_15_min |
+----+---------+--------------------------+-------------------------+----------------+
1 row in set (0.00 sec)
The where clause is evaluated last in this query and is free to choose which one it wants from the result set - in this case always the first.
if the query is changed to test test the payment_reminder_1_date
update new_reminders n join (select * from old_reminder order by applicant_id,`date`) old on old.applicant_id = n.user_id
SET
enumstr = old.type,
payment_reminder_1_date =
case
when old.type in ('payment_15_min','payment_1_day','payment_3_day') then old.date
else '2017-01-01'
end
WHERE applicant_id = 123 and n.payment_reminder_1_date <> old.`date`
Then you get something more like what you hope for
+----+---------+--------------------------+-------------------------+---------------+
| id | user_id | payment_reminder_1_count | payment_reminder_1_date | enumstr |
+----+---------+--------------------------+-------------------------+---------------+
| 1 | 123 | NULL | 2018-01-02 00:00:00 | payment_1_day |
+----+---------+--------------------------+-------------------------+---------------+
1 row in set (0.00 sec)
But I don't think this is actually what you are looking for and I would suggest a cursor might be the way forward.