ALTER Keyword usage

Use	Syntax	Example
Rename table	ALTER TABLE old_table_name RENAME TO new_table_name;	ALTER TABLE employees RENAME TO staff;
Add column	ALTER TABLE table_name ADD column_name datatype;	ALTER TABLE employees ADD salary DECIMAL(10,2);
Drop column	ALTER TABLE table_name DROP COLUMN column_name;	ALTER TABLE employees DROP COLUMN salary;
Rename column	ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name;	ALTER TABLE employees RENAME COLUMN name TO full_name;
Modify datatype	ALTER TABLE table_name MODIFY column_name new_datatype; (MySQL)	ALTER TABLE employees MODIFY salary BIGINT;
Add primary key	ALTER TABLE table_name ADD PRIMARY KEY (column_name);	ALTER TABLE employees ADD PRIMARY KEY (employee_id);
Drop primary key	ALTER TABLE table_name DROP PRIMARY KEY;	ALTER TABLE employees DROP PRIMARY KEY;
Add foreign key	ALTER TABLE child_table ADD CONSTRAINT fk_name FOREIGN KEY (child_column) REFERENCES parent_table(parent_column);	ALTER TABLE orders ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(id);
Drop foreign key	ALTER TABLE table_name DROP FOREIGN KEY fk_name;	ALTER TABLE orders DROP FOREIGN KEY fk_customer;

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