I need to create an external table in hiveql with the output from a SELECT clause. Every time when the HiveQL is ran the table should be dropped and recreated . When we drop an external table only the table structure is getting dropped but not the data files from HDFS location. How to achieve this?
Create Table As Select (CTAS) has restrictions. One of them is that target table cannot be External.
You have these options:
Create external table once, then INSERT OVERWRITE
INSERT OVERWRITE TABLE tablename1 [PARTITION (partcol1=val1, partcol2=val2 ...) select_statement1 FROM from_statement;
Use managed table, then you can DROP TABLE, then CREATE TABLE ... as SELECT
See also answer about skipTrash and auto.purge property.
Related
I have created table using this statement:
CREATE TABLE tablename STORED AS PARQUET AS (SELECT ...)
How can i recalculate it without DROP TABLE - CREATE TABLE flow?
In Impala, The INSERT INTO syntax appends data to a table. The existing data files are left as-is, and the inserted data is put into one or more new data files.
The INSERT OVERWRITE syntax replaces the data in a table. Currently, the overwritten data files are deleted immediately; they do not go through the HDFS trash mechanism.
So If you want to replace the data in the table tablename without undergoing drop table and create table, you can run a query like this
INSERT OVERWRITE TABLE tablename SELECT * from <source_tablename>;
I have an external table, now I want to add partitions to it. I have 224 unique city id's and I want to just write alter table my_table add partition (cityid) location /path; but hive complains, saying that I don't provide anything for the city id value, it should be e.g. alter table my_table add partition (cityid=VALUE) location /path;, but I don't want to run alter table commands for every value of city id, how can I do it for all id's in one go?
This is what hive command line looks like:
hive> alter table pavel.browserdata add partition (cityid) location '/user/maria_dev/data/cityidPartition';
FAILED: ValidationFailureSemanticException table is not partitioned but partition spec exists: {cityid=null}
Partition on physical level is a location (separate location for each value, usually looks like key=value) with data files. If you already have partitions directory structure with files, all you need is to create partitions in Hive metastore, then you can point your table to the root directory using ALTER TABLE SET LOCATION, then use MSCK REPAIR TABLE command. The equivalent command on Amazon Elastic MapReduce (EMR)'s version of Hive is: ALTER TABLE table_name RECOVER PARTITIONS. This will add Hive partitions metadata. See manual here: RECOVER PARTITIONS
If you have only not-partitioned table with data in it's location, then adding partitions will not work because the data needs to be reloaded, you need to:
Create another partitioned table and use insert overwrite to load partition data using dynamic partition load:
set hive.exec.dynamic.partition=true;
set hive.exec.dynamic.partition.mode=nonstrict;
insert overwrite table2 partition(cityid)
select col1, ... colN,
cityid
from table1; --partitions columns should be last in the select
This is quite efficient way to reorganize your data.
After this you can delete source table and rename your target table.
There is one external table in Hive. It has data. When I do insert overwrite it updates files at location which table points. But table data is not updated when executing select *.
I tried lot but couldn't find answer for this issue. I did my work using alternative method. I am sharing here so that if someone facing same issue, he can use this.
1.
create table target_table_name like source_table_name;
2.
insert overwrite table target_table_name partition(partition_column_name) select * from source_table_name;
3.create external table another_table_name like source_table_name stored as file_format_of_source_table location 'location_of_source_table';
4.msck repair table another_table;
5.Then you can drop source_table and rename another_table to source_table_name.
I am using HDInsight and need to delete my clusters when I am finished running queries. However, I need the data I gather to survive for another day. I am working on queries that would create calculated columns from table1 and insert them into table2. First I wanted a simple test to copy the rows. Can you create an external table from a select statement?
drop table if exists table2;
create external table table2 as
select *
from table1
STORED AS TEXTFILE LOCATION 'wasb://{container name}#{storage name}.blob.core.windows.net/';
yes but you have to seperate it into two commands. First create the external table then fill it.
create external table table2(attribute STRING)
STORED AS TEXTFILE
LOCATION 'table2';
INSERT OVERWRITE TABLE table2 Select * from table1;
The schema of table2 has to be the same as the select query, in this example it consists only of one string attribute.
I know this is too stale question but here is the solution.
CREATE EXTERNAL TABLE table2
STORED AS textfile
LOCATION wasb://....
AS SELECT * FROM table1
Since create external table with "as select" clause is not supported in Hive, first we need to create external table with complete DDL command and then load the data into the table. Please go through this for different data format supports.
create external table table_ext(col1 typ1,...)
STORED AS ORC
LOCATION 'table2'; // optional if not provided then default location is used
INSERT OVERWRITE TABLE table_ext Select * from table1;
make sure table_ext has same DDL as table1.
I have created an external table in Hive with at this location :
CREATE EXTERNAL TABLE tb
(
...
)
PARTITIONED BY (datehour INT)
ROW FORMAT SERDE 'com.cloudera.hive.serde.JSONSerDe'
LOCATION '/user/cloudera/data';
The data is present in the folder but when I query the table, it returns nothing. The table is structured in a way that it fits the data structure.
SELECT * FROM tb LIMIT 3;
Is there a kind of permission issue with Hive tables: do specific users have permissions to query some tables?
Do you know some solutions or workarounds?
You have created your table as partitioned table base on column datehour, but you are putting your data in /user/cloudera/data. Hive will look for data in /user/cloudera/data/datehour=(some int value). Since it is an external table hive will not update the metastore. You need to run some alter statement to update that
So here are the steps for external tables with partition:
1.) In you external location /user/cloudera/data, create a directory datehour=0909201401
OR
Load data using: LOAD DATA [LOCAL] INPATH '/path/to/data/file' INTO TABLE partition(datehour=0909201401)
2.) After creating your table run a alter statement:
ALTER TABLE ADD PARTITION (datehour=0909201401)
Hope it helps...!!!
When we create an EXTERNAL TABLE with PARTITION, we have to ALTER the EXTERNAL TABLE with the data location for that given partition. However, it need not be the same path as we specify while creating the EXTERNAL TABLE.
hive> ALTER TABLE tb ADD PARTITION (datehour=0909201401)
hive> LOCATION '/user/cloudera/data/somedatafor_datehour'
hive> ;
When we specify LOCATION '/user/cloudera/data' (though its optional) while creating an EXTERNAL TABLE we can take some advantage of doing repair operations on that table. So when we want to copy the files through some process like ETL into that directory, we can sync up the partition with the EXTERNAL TABLE instead of writing ALTER TABLE statement to create another new partition.
If we already know the directory structure of the partition that HIVE would create, we can simply place the data file in that location like '/user/cloudera/data/datehour=0909201401/data.txt' and run the statement as shown below:
hive> MSCK REPAIR TABLE tb;
The above statement will sync up the partition to the hive meta store of the table "tb".