What SQL command is primarily used for data retrieval?

The primary SQL command used for data retrieval is the SELECT statement. This command allows users to query data from one or more tables in a database, returning the results in the form of a result set. The SELECT command can also be customized with various clauses such as WHERE, ORDER BY, and GROUP BY to filter, sort, or group the retrieved data based on user-defined conditions.

In contrast, the other commands serve different purposes within SQL. ALTER is used to modify the structure of an existing database table, affecting its columns, constraints, or data types. CREATE is utilized to generate new database objects, such as tables or databases themselves. DROP, on the other hand, is responsible for removing existing database objects, which can include entire tables or databases. Each of these commands operates within the realm of data structure and management rather than data retrieval, highlighting the unique role of SELECT in querying information from a database.