USE statement
The USE statement switches the current session to a specified
database. The current database is where any CREATE TABLE,
INSERT, SELECT, or other statements act when you specify a
table or other object name, without prefixing it with a database name. The new current database
applies for the duration of the session or unti another USE statement is
executed.
Syntax:
USE db_name
By default, when you connect to an Impala instance, you begin in a database named default.
Usage notes:
Switching the default database is convenient in the following situations:
-
To avoid qualifying each reference to a table with the database name. For example,
SELECT * FROM t1 JOIN t2rather thanSELECT * FROM db.t1 JOIN db.t2. - To do a sequence of operations all within the same database, such as creating a table, inserting data, and querying the table.
To start the impala-shell interpreter and automatically issue a USE
statement for a particular database, specify the option -d db_name for
the impala-shell command. The -d option is useful to run SQL scripts,
such as setup or test scripts, against multiple databases without hardcoding a USE statement
into the SQL source.
Examples:
See the CREATE DATABASE statement for examples covering CREATE
DATABASE, USE, and DROP DATABASE.
Cancellation: Cannot be cancelled.
HDFS permissions: This statement does not touch any HDFS files or directories, therefore no HDFS permissions are required.
