![]() If you cannot get out of that then consider leaving it as a NULL-able column. With an ORM, you normally create a class that represents a table in a SQL database, each attribute of the class represents a column, with a name and a type. In the case where you add it is NULL-able and backfill it, making the column NOT NULL will still lock the table while the engine checks every row to make sure it is NOT NULL so you'll still need some downtime. Pick a time when you can add the column in the way Gail showed, maybe as part of a scheduled reboot or other downtime, or look at Chris' method where the column is added as NULL-able but chunk the update to fill in the column with 0's into small batches of 10K rows or so at a time so you do not block too many users while you backfill the data. You should be more concerned that when you add the column that no data is lost in the process. The main drawbacks of MyISAM are that it doesnt support transactions or enforce foreign-key constraints. The table in question receives both a lot of reads and writes, this is my concern. Good point completely overlooked the fact that the table will be written to during the read to the new table :ermm: douh! The method Gail showed is your best bet for performance and protect against data loss unless you are OK with losing data or you know your table is truly only ever read. CHECK (expr) As of MySQL 8.0.16, CREATE TABLE permits the core features of table and column CHECK constraints, for all storage engines. ![]() ![]() MySQL Constraints classified into two types: - Column level and. ![]() Is it only for reads? If you do not lock the table the "copy" and "rename" steps then if anyone modifies data in the source table during the process you could lose data when you drop the old table and rename the new one to take its place. MySQL Constraint is used to define Rules to allow or restrict what values stored in columns. Yes definitely slower and more work but it wont lock the table.Įrr, I presume you re worried about locking the table because people are using it. The UNIQUE constraint ensures that a columns values remain unique or individual among all the other values in the column. You can do that, it'll likely be slower than the ALTER and far more work, but it'll do the job. That is why I was looking into creating a new table with the addtional column then moving the data etc and finally doing a table rename ![]()
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