How Does it work?Ī new concept of row version is introduced in table metadata. Multiple columns can be ADD/DROP in a single ALTER TABLE STATEMENT. SyntaxĪLTER TABLE ADD COLUMN /, ALGORITHM=INSTANT ĪLTER TABLE DROP COLUMN, ALGORITHM=INSTANT ĪLGORITHM=INSTANT is optional here as, by default, all ADD/DROP columns are done with ALGORITHM=INSTANT. In other words, the time taken to ADD/DROP new/old column(s) to/from a table with 1 row would be the same as time taken to ADD/DROP new/old column(s) to/from a table having 100M rows. Therefore, ADD/DROP COLUMN operations aren't dependent on the table size anymore. " don't touch any row but update the metadata only". This design also follow the same idea i.e. DROP existing column(s) from "any position" from a table with ALGORITHM=INSTANT.ADD new column(s) at "any position" to a table with ALGORITHM=INSTANT.And this design can be easily consumed by the ADD COLUMN, ALGORITHM=INSTANT as well. Finally we came up with a new design which enables user to DROP column(s) from "any position" from a table with ALGORITHM=INSTANT. During this, we also had the limitations of earlier INSTANT ADD implementation in mind. We went back on whiteboard discussion to design something to make even the DROP COLUMN "instant". Mysql> alter table t1 drop column c2, algorithm=instant Mysql> alter table t1 add column c3 char (10) FIRST, ALGORITHM=INSTANT Mysql> alter table t1 add column c3 char (10) AFTER c1, ALGORITHM=INSTANT ĮRROR 1845 (0A000): ALGORITHM=INSTANT is not supported for this operation. Mysql> create table t1 (c1 char (10), c2 char (10)) Type '\c' to clear the current input statement. Other names may be trademarks of their respective Oracle is a registered trademark of Oracle Corporation and / or itsĪffiliates. Server version: 8.0.28 Source distributionĬopyright (c) 2000, 2022, Oracle and / or its affiliates. ADD COLUMN " had behaved in MySQL 8.0.28 (before MySQL 8.0.29 introduced the optimization, described in this article): This feature enables users to ADD new columns "INSTANTLY" to a table irrespective of table size. In other words, " don't touch any row but update the metadata only" is the core idea we came up with to solve it.Īcknowledging users requests, an early implementation of ADD COLUMN with ALGORITHM=INSTANT was added in MySQL 8.0.12. Therefore, if we could come up with a mechanism in which this "need" is omitted and we could achieve ADD/DROP COLUMN by just modifying the metadata. The root cause of problem statement is clear : " the need of modifying all existing records in the table for ADD/DROP COLUMN". And that's why o ne of the most asked feature requests from MySQL users is to have capability to ADD/DROP new/existing column(s) to/from an InnoDB Table, instantly. InnoDB, the default storage engine for MySQL, is not an exception here. And, as the number of rows in the table increases, time taken to modify all existing rows to reflect the table definition change because of ADD/DROP columns also increases. Now, if a new column is to be added or an old column is to be dropped from a table, the contents of existing rows should be changed to reflect the correct values of columns present in the table. It should be noted that newly added column is filled with NULL values.In databases, rows are persisted on disk and for every row, columns' value are stored on disk. Sqlite> ALTER TABLE OLD_COMPANY ADD COLUMN SEX char(1) ĬOMPANY table is now changed and following will be the output from SELECT statement. Now, let's try to add a new column in OLD_COMPANY table as follows − The above SQLite statement will rename COMPANY table to OLD_COMPANY. Sqlite> ALTER TABLE COMPANY RENAME TO OLD_COMPANY Now, let's try to rename this table using ALTER TABLE statement as follows − Ĭonsider the COMPANY table with the following records − Syntaxįollowing is the basic syntax of ALTER TABLE to RENAME an existing table.ĪLTER TABLE database_name.table_name RENAME TO new_table_name įollowing is the basic syntax of ALTER TABLE to add a new column in an existing table.ĪLTER TABLE database_name.table_name ADD COLUMN column_def. There is no other operation supported by ALTER TABLE command in SQLite except renaming a table and adding a column in an existing table. You can rename a table using ALTER TABLE statement and additional columns can be added in an existing table using ALTER TABLE statement. SQLite ALTER TABLE command modifies an existing table without performing a full dump and reload of the data.
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