How is the alter statement used in SQL?

The ALTER statement in SQL is used to modify the structure or properties of a database table. It can perform the following actions:

1. Add Column: Use the ALTER TABLE command with the ADD clause to add a new column to an existing table.

Option:
2. Modifying columns: Use the ALTER TABLE command and ALTER COLUMN clause to change the data type, length, or other properties of existing columns in a table.

3. To delete a column: Use the ALTER TABLE command with the DROP COLUMN clause to remove a column from a table.

4. Rename a table: Use the ALTER TABLE command with the RENAME TO clause to specify a new name for the table.

5. Adding constraints: Use the ALTER TABLE command and the ADD CONSTRAINT clause to add new constraints to a table, such as primary keys, uniqueness constraints, or foreign key constraints.

6、To modify constraints: Use the ALTER TABLE command and ALTER CONSTRAINT clause to change the properties or behaviors of existing constraints in a table.

Removing constraints: You can delete a constraint from a table using the ALTER TABLE command with the DROP CONSTRAINT clause.

It is important to be cautious when executing the `ALTER` statement, and carefully consider the impact on existing data to ensure that the modification operation will not compromise data integrity or result in data loss.