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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="use"> |
| |
| <title>USE Statement</title> |
| <titlealts audience="PDF"><navtitle>USE</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="SQL"/> |
| <data name="Category" value="Databases"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| <indexterm audience="hidden">USE statement</indexterm> |
| Switches the current session to a specified database. The <term>current database</term> is where any |
| <codeph>CREATE TABLE</codeph>, <codeph>INSERT</codeph>, <codeph>SELECT</codeph>, 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 <codeph>USE</codeph> statement is executed. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/syntax_blurb"/> |
| |
| <codeblock>USE <varname>db_name</varname></codeblock> |
| |
| <p> |
| By default, when you connect to an Impala instance, you begin in a database named <codeph>default</codeph>. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| |
| <p> |
| Switching the default database is convenient in the following situations: |
| </p> |
| |
| <ul> |
| <li> |
| To avoid qualifying each reference to a table with the database name. For example, <codeph>SELECT * FROM t1 |
| JOIN t2</codeph> rather than <codeph>SELECT * FROM db.t1 JOIN db.t2</codeph>. |
| </li> |
| |
| <li> |
| To do a sequence of operations all within the same database, such as creating a table, inserting data, and |
| querying the table. |
| </li> |
| </ul> |
| |
| <p> |
| To start the <cmdname>impala-shell</cmdname> interpreter and automatically issue a <codeph>USE</codeph> |
| statement for a particular database, specify the option <codeph>-d <varname>db_name</varname></codeph> for |
| the <cmdname>impala-shell</cmdname> command. The <codeph>-d</codeph> option is useful to run SQL scripts, |
| such as setup or test scripts, against multiple databases without hardcoding a <codeph>USE</codeph> statement |
| into the SQL source. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/example_blurb"/> |
| |
| <p> |
| See <xref href="impala_create_database.xml#create_database"/> for examples covering <codeph>CREATE |
| DATABASE</codeph>, <codeph>USE</codeph>, and <codeph>DROP DATABASE</codeph>. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/cancel_blurb_no"/> |
| |
| <p conref="../shared/impala_common.xml#common/permissions_blurb_no"/> |
| |
| <p conref="../shared/impala_common.xml#common/related_info"/> |
| |
| <p> |
| <xref href="impala_create_database.xml#create_database"/>, |
| <xref href="impala_drop_database.xml#drop_database"/>, <xref href="impala_show.xml#show_databases"/> |
| </p> |
| </conbody> |
| </concept> |