Changing the schema

Changing a table's structure

A table's design is not fixed. ALTER TABLE … ADD adds a new column to an existing table:

ALTER TABLE product ADD weight DECIMAL(5, 2);

Existing rows get NULL in the new column until you fill them in.

DROP TABLE deletes a whole table — its structure and all its rows:

DROP TABLE product;

This cannot be undone, so use it with care. Dropping a table that other tables reference can break referential integrity.

Add a new column weight of type DECIMAL(5, 2) to the product table using ALTER TABLE.

ALTER TABLE product ADD ...;

Click Run to see the output here.

Delete the entire product table with DROP TABLE. (Afterwards only customer and orders remain.)

DROP TABLE ...;

Click Run to see the output here.