DROP TABLE statement
DROP TABLE statement removes an Impala table. Also removes the
underlying HDFS data files for internal tables, although not for external tables.
DROP TABLE [IF EXISTS] [db_name.]table_name [PURGE]
IF EXISTS clause:
IF EXISTS clause makes the statement succeed whether or not the table exists.
If the table does exist, it is dropped; if it does not exist, the statement has no effect. This capability is
useful in standardized setup scripts that remove existing schema objects and create new ones. By using some
IF EXISTS for the
DROP statements and
EXISTS clauses for the
CREATE statements, the script can run successfully the first
time you run it (when the objects do not exist yet) and subsequent times (when some or all of the objects do
PURGE keyword, available in Impala 2.3 and higher,
causes Impala to remove the associated HDFS data files immediately, rather than going
through the HDFS trashcan mechanism. Use this keyword when dropping a table if it is crucial
to remove the data as quickly as possible to free up space, or if there is a problem with
the trashcan, such as the trash cannot being configured or being in a different HDFS
encryption zone than the data files.
Statement type: DDL
By default, Impala removes the associated HDFS directory and data files for the table. If you issue a
DROP TABLE and the data files are not deleted, it might be for the following reasons:
- If the table was created with the
EXTERNALclause, Impala leaves all files and directories untouched. Use external tables when the data is under the control of other Hadoop components, and Impala is only used to query the data files from their original locations.
- Impala might leave the data files behind unintentionally, if there is no HDFS location
available to hold the HDFS trashcan for the
Make sure that you are in the correct database before dropping a table, either by issuing a
USE statement first or by using a fully qualified name
If you intend to issue a
DROP DATABASE statement, first issue
statements to remove all the tables in that database.
create database temporary; use temporary; create table unimportant (x int); create table trivial (s string); -- Drop a table in the current database. drop table unimportant; -- Switch to a different database. use default; -- To drop a table in a different database... drop table trivial; ERROR: AnalysisException: Table does not exist: default.trivial -- ...use a fully qualified name. drop table temporary.trivial;
Amazon S3 considerations:
DROP TABLE statement can remove data
files from S3 if the associated S3 table is an internal table. In Impala 2.6 and higher, as
part of improved support for writing to S3, Impala also removes the associated folder when
dropping an internal table that resides on S3.
- Use native Hadoop techniques, such as
hadoop fs -cpor
INSERTin Impala or Hive to create data files in S3.
- Use the
DROP TABLEwhen dropping internal (managed) tables.
PURGEclause, the data files are deleted immediately, skipping the expensive S3A trashcan operation.
In Impala 2.6 and higher, Impala DDL
statements such as
DROP DATABASE CASCADE,
DROP TABLE, and
TABLE [ADD|DROP] PARTITION can create or remove folders as needed in the Amazon
S3 system. Prior to Impala 2.6, you had to create folders yourself and point Impala
database, tables, or partitions at them, and manually remove folders when no longer needed.
See Impala with Amazon S3 for details about reading and writing S3 data
Cancellation: Cannot be cancelled.
For an internal table, the user ID that the impalad daemon runs under,
impala user, must have write
permission for all the files and directories that make up the table.
For an external table, dropping the table only involves changes to metadata in the metastore database. Because Impala does not remove any HDFS files or directories when external tables are dropped, no particular permissions are needed for the associated HDFS files or directories.
Kudu tables can be managed or external, the same as with HDFS-based
tables. For a managed table, the underlying Kudu table and its data
are removed by
DROP TABLE. For an external table,
the underlying Kudu table and its data remain after a