What function does the ALTER statement serve in SQL?

The ALTER statement in SQL is specifically designed to change the structure of an existing table. This may involve adding new columns, modifying existing ones, or dropping columns from the table. It enables the user to adjust the table's schema without having to recreate it, which can be particularly useful in managing the database structure over time as requirements change.

For instance, if a new data requirement emerges that necessitates the addition of a field to store additional information, one would use the ALTER statement to make this adjustment directly to the existing table rather than creating a new one, thereby preserving existing data and relationships.

The other functions mentioned in the options relate to different SQL commands. For instance, retrieving specific data from a database typically involves the SELECT statement, deleting rows is accomplished using the DELETE statement, and creating new tables is performed with the CREATE TABLE statement. Each of these is distinct and serves its own purpose within SQL, highlighting the specialized role that the ALTER statement plays in modifying existing table structures.