We will again execute the DESC saledetails. CALL addColumnToTable () is executed whenever we want to run the procedure addColumnToTable. ALTER TABLE statement will ADD the new column to the table. In case the IF condition is not true, the statement after THEN is executed. You can specify explicit ALGORITHM=INSTANT LOCK=NONE parameters, and if an instant schema change isn't possible, MySQL will fail with an error instead of falling back to INPLACE or COPY. Database () function retrieves the current schema from the MySQL server. CREATE TABLE example ( examplecolumn INT COMMENT 'This is an example column', anothercolumn2 VARCHAR (100) COMMENT 'One more column' ) COMMENT'This is a comment about table' so in your case. It's not a magical solution, it has limitations and side-effects - it can only be the last column, the table must not have a full text index, etc - but should help in many cases. If it's easy for you to create replicas, like if you're hosted at Amazon RDS, you may create a master-master replica, run the alter table there, let it get back in sync, and switch instances after finished.Īs others mentioned, MySQL 8.0 INNODB added support for instant column adds. If you don't use foreign keys and it's slow because you have a lot of indexes, it might be faster for you to create a copy of the table with the changes you need but no secondary indexes, populate it with the data, and create all indexes with a single alter table at the end. Follow this below MySQL command: CREATE TABLE IF. Backup your data first! This is the easiest solution, but may not work in all cases. Now lets have a look on more examples to add column in MySQL: 1. You may use the pt-online-schema-change, from Percona toolkit. It doesn't matter if it's slow, it only matters that other clients can't perform queries until your ALTER TABLE is finished. Long answer: your real problem isn't really performance, but the lock time. It is also shown in the COLUMNCOMMENT column of the Information Schema COLUMNS table. The comment is displayed by the SHOW CREATE TABLE and SHOW FULL COLUMNS statements. You may add ENUM and SET values instantly, and you may add secondary indexes while locking only for writes, but altering table structure always requires a table copy. A comment for a column can be specified with the COMMENT option, up to 1024 characters long. At this point, it must acquire an exclusive lock. Are there other ways to improve performance of adding a column to a large table? From the docs on MySQL 8, The exception referred to earlier is that ALTER TABLE blocks reads (not just writes) at the point where it is ready to clear outdated table structures from the table and table definition caches.
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