Quick Reference
The ALTER keyword adds, deletes, or modifies columns in a table. It can also add and delete various constraints in a table.
ALTER TABLE
The following adds the last_name column to the Customers table.
ALTER TABLE Customers
ADD last_name varchar(255);The following deletes the last_name column from the Customers table.
ALTER TABLE Customers
DROP COLUMN last_name;ALTER COLUMN
The following changes the data type of the column named start_date in the Customers table to type year.
ALTER TABLE Customers
ALTER COLUMN start_date year;SQL Notes:
- Any work being done to modify the structure of a database or delete tables or the the database itself should only be done after making a recent backup
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