Athena uses Apache Hive DDL to define tables. You can run DDL statements using the Athena console, with an ODBC or JDBC driver, through the API, or using the Athena create table wizard. If you use the Data Catalog with Athena, you can also use AWS Glue crawlers to automatically infer schemas and partitions. An AWS Glue crawler connects to a data store, progresses through a prioritized list of classifiers to extract the schema of your data and other statistics, and then populates the Data Catalog with this metadata. Crawlers can run periodically to detect the availability of new data and changes to existing data, including table definition changes. Crawlers automatically add new tables, new partitions to existing table, and new versions of table definitions. You can customize AWS Glue crawlers to classify your own file types.
When you create a new table schema in Athena, the schema is stored in the Data Catalog and used when running queries, but it does not modify your data in S3. Athena uses an approach known as schema-on-read, which allows you to project your schema onto your data when you run a query. This decreases the need for any data loading or transformation. Learn more about creating tables.