Which command type is not classified as a Data Definition Language (DDL) command?

Data Definition Language (DDL) commands are used to define and manage all structures in a database, essentially setting up and modifying the database schema. This includes creating, altering, and deleting tables and schemas themselves.

The command that fits this definition is the UPDATE command, which is primarily used for modifying the data within existing records of a table, rather than altering the structure of the database itself. By contrast, commands like CREATE TABLE, ALTER TABLE, and DROP TABLE are all focused on defining or modifying the structure of the database. CREATE TABLE establishes a new table, ALTER TABLE modifies an existing table's structure, and DROP TABLE removes an existing table entirely.

Therefore, the UPDATE command stands apart from the others, as it does not deal with schema definition or structure but instead with the contents of the database.