Athena: Using CREATE TABLE AS SELECT (CTAS)
Introduction
A CREATE TABLE AS SELECT (CTAS) query creates a new table in Athena from the results of a SELECT statement from another query. This can be a useful way to create a new table with a subset of data from an existing table, or to combine data from multiple tables into a single table.
CTAS queries are supported by most major relational database systems, including PostgreSQL, MySQL, and Oracle. In Athena, CTAS queries are supported via the Presto engine, which is a high-performance distributed SQL query engine. This makes CTAS queries a powerful and flexible tool for working with data in Athena.
Examples
The following examples show how to use CTAS queries in Athena:
-- Create a new table called `my_new_table` from the results of a SELECT statement from the `my_existing_table` table CREATE TABLE my_new_table AS SELECT * FROM my_existing_table WHERE some_column > 10; -- Create a new table called `my_new_table` from the results of a SELECT statement that combines data from multiple tables CREATE TABLE my_new_table AS SELECT * FROM my_existing_table1 JOIN my_existing_table2 ON my_existing_table1.id = my_existing_table2.id;
Syntax
The syntax for a CTAS query in Athena is as follows:
CREATE TABLE [IF NOT EXISTS] table_name AS SELECT column_list FROM source_table [WHERE condition];
- table_name is the name of the new table to be created.
- column_list is a comma-separated list of the columns to be included in the new table.
- source_table is the name of the table from which the data will be selected.
- condition is an optional WHERE clause that can be used to filter the data that is selected.
Considerations
When using CTAS queries, there are a few important considerations to keep in mind:
- The new table will be created in the same database as the source table.
- The new table will have the same schema as the source table, unless a column list is specified.
- The new table will not be populated with data until the CTAS query has been executed.
- CTAS queries can be expensive to execute, especially if the source table is large.
Conclusion
CTAS queries are a powerful and flexible tool for working with data in Athena. They can be used to create new tables, combine data from multiple tables, and filter data based on specific criteria. By understanding the syntax and considerations for using CTAS queries, you can use them to effectively manage your data and get the most out of Athena.
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