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ALTER TABLE `tbl_student` ADD UNIQUE student_unique_index (`student_id`) Here, student_unique_index is the index name assigned to student_id and creates an index for which values must be unique (here null can be accepted).
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;
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
With the ALTER TABLE statement, you can rename tables, rename columns, add columns, drop columns, modify column properties, etc. ALTER TABLE syntax ALTER TABLE table_name [ alter_action options ], ...
Example. To improve performance one might want to add indexes to columns. ALTER TABLE TABLE_NAME ADD INDEX `index_name` (`column_name`) altering to add composite (multiple column) indexes. ALTER TABLE TABLE_NAME ADD INDEX `index_name` (`col1`,`col2`)
26 Ιαν 2024 · Adding an index in MySQL 8 typically involves using the CREATE INDEX command. Here’s the basic syntax: CREATE INDEX index_name ON table_name (column1, column2, ...); For instance, to create a single-column index: And here’s how you might create a multi-column index:
