How to create a partition in MySql if it doesn't exist? - mysql

Question

I have a partitioned table, in which I'm inserting data from a stored procedure,
I have partitioning on the table by a column named year,
The stored procedure is able to insert data into the partitioned table properly.
But now I have a case where inserts might happen, for which partitions may not be present,
I need a solution to find if a particular partition name exists for the table.
Eg. My table name is backups
I have 3 Partitions for now -
2018, 2019 and 2020
But in the year 2021 which the stored procedure runs,
there may not be a partition for the year
So I wish my stored procedure handle the checking and creation of the partition at run time.
Following is my table structure -
Partition creation query -
ALTER TABLE backups
partition by list columns(year)
(partition backup_2018 values IN (2018),
partition backup_2019 values IN (2019),
partition backup_2020 values IN (2020));
Following is my stored procedure -
CREATE DEFINER=`root`#`localhost` PROCEDURE `daily_backup`()
BEGIN
DECLARE backuptime INT;
#Need Partition checking and creation here
SET backuptime = UNIX_TIMESTAMP(CONCAT(DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-%d'), INTERVAL 1 DAY),' 23:59:59'));
INSERT into backups
(user_id, latest_transaction_id, balance, last_transaction_timestamp, last_transaction_date, snapshot_date, year)
SELECT
T2.user_id,
T2.transaction_id AS latest_transaction_id,
T2.new_balance AS balance,
T2.created_date AS last_transaction_timestamp,
DATE_FORMAT(FROM_UNIXTIME(T2.created_date), '%Y-%m-%d %I:%i:%S') AS last_transaction_date,
DATE_FORMAT(NOW(), '%Y-%m-%d') AS snapshot_date,
DATE_FORMAT(NOW(), '%Y') AS year
FROM
(SELECT
user_id, MAX(transaction_id) maxTransID
FROM
transaction
WHERE
created_date < #backuptime
GROUP BY user_id) Tmp
JOIN
transaction T2 ON Tmp.MaxTransID = T2.Transaction_ID;
END

Answer 1

I suggest partitioning using RANGE COLUMNS instead of LIST COLUMNS. That way you have the option of adding a last column for any years beyond the partitions you have defined so far.
ALTER TABLE backups
partition by range columns(year)
(partition backup_2018 values LESS THAN (2019),
partition backup_2019 values LESS THAN (2020),
partition backup_2020 values LESS THAN (2021),
partition backup_other values LESS THAN MAXVALUE);
As you get closer to the end of 2020, you'd use ALTER TABLE backups REORGANIZE PARTITION backup_other INTO ( ...new partitions... ) to split the last partition and make new partitions for subsequent years.
See https://dev.mysql.com/doc/refman/5.7/en/partitioning-management-range-list.html for more details.
If you forget, no harm done, your data will just fill up backup_other for a while until you remember to reorganize. It's to your advantage though to do it proactively, because reorganizing an empty partition is quick, and reorganizing a partition with data in it will take more time.