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Indexes of two types can be added: when you define a primary key, MySQL will take it as index by default. Explanation. Primary key as index. Consider you have a tbl_student table and you want student_id as primary key: ALTER TABLE `tbl_student` ADD PRIMARY KEY (`student_id`)
After an ALTER TABLE statement, it may be necessary to run ANALYZE TABLE to update index cardinality information. See Section 15.7.7.23, “SHOW INDEX Statement”. The ALTER INDEX operation permits an index to be made visible or invisible. An invisible index is not used by the optimizer.
ALTER TABLE t2 MODIFY a TINYINT NOT NULL, CHANGE b c CHAR(20); To add a new TIMESTAMP column named d: ALTER TABLE t2 ADD d TIMESTAMP; To add an index on column d and a UNIQUE index on column a: ALTER TABLE t2 ADD INDEX (d), ADD UNIQUE (a); To remove column c: ALTER TABLE t2 DROP COLUMN c;
Besides the CREATE INDEX statement, you can use the ALTER TABLE statement to add a functional index to a table: ALTER TABLE table_name ADD INDEX index_name((fn)); Code language: SQL (Structured Query Language) (sql) MySQL functional index example. We’ll use the orders table from the sample database:
20 Απρ 2024 · ALTER TABLE is a SQL statement used to modify the structure of a table, such as adding, modifying, or dropping columns, constraints, or indexes.
The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. The ALTER TABLE statement is also used to add and drop various constraints on an existing table. ALTER TABLE - ADD Column
In this article, we described how to use the ALTER TABLE statement modify a table, including: adding columns, deleting columns, modifying columns, renaming columns, renaming tables, setting primary keys, etc.
