Hive Data Types

 Complex Data Type

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If you’re already familiar with SQL then you may well be thinking about how to add Hadoop skills to your toolbelt as an option for data processing.

From a querying perspective, using Apache Hive provides a familiar interface to data held in a Hadoop cluster and is a great way to get started. Apache Hive is data warehouse infrastructure built on top of Apache Hadoop for providing data summarization, ad-hoc query, and analysis of large datasets. It provides a mechanism to project structure onto the data in Hadoop and to query that data using a SQL-like language called HiveQL (HQL).

If you really want to get to grips with Hive, then take a look at the full language manual.

Retrieving Information

Function	MySQL	Hive
Retrieving Information (General)	SELECT from_columns FROM table WHERE conditions;	SELECT from_columns FROM table WHERE conditions;
Retrieving All Values	SELECT * FROM table;	SELECT * FROM table;
Retrieving Some Values	SELECT * FROM table WHERE rec_name = "value";	SELECT * FROM table WHERE rec_name = "value";
Retrieving With Multiple Criteria	SELECT * FROM TABLE WHERE rec1 = "value1" AND rec2 = "value2";	SELECT * FROM TABLE WHERE rec1 = "value1" AND rec2 = "value2";
Retrieving Specific Columns	SELECT column_name FROM table;	SELECT column_name FROM table;
Retrieving Unique Output	SELECT DISTINCT column_name FROM table;	SELECT DISTINCT column_name FROM table;
Sorting	SELECT col1, col2 FROM table ORDER BY col2;	SELECT col1, col2 FROM table ORDER BY col2;
Sorting Reverse	SELECT col1, col2 FROM table ORDER BY col2 DESC;	SELECT col1, col2 FROM table ORDER BY col2 DESC;
Counting Rows	SELECT COUNT(*) FROM table;	SELECT COUNT(*) FROM table;
Grouping With Counting	SELECT owner, COUNT(*) FROM table GROUP BY owner;	SELECT owner, COUNT(*) FROM table GROUP BY owner;
Maximum Value	SELECT MAX(col_name) AS label FROM table;	SELECT MAX(col_name) AS label FROM table;
Selecting from multiple tables (Join same table using alias w/”AS”)	SELECT pet.name, comment FROM pet, event WHERE pet.name = event.name;	SELECT pet.name, comment FROM pet JOIN event ON (pet.name = event.name)

Metadata

Function	MySQL	Hive
Selecting a database	USE database;	USE database;
Listing databases	SHOW DATABASES;	SHOW DATABASES;
Listing tables in a database	SHOW TABLES;	SHOW TABLES;
Describing the format of a table	DESCRIBE table;	DESCRIBE (FORMATTED|EXTENDED) table;
Creating a database	CREATE DATABASE db_name;	CREATE DATABASE db_name;
Dropping a database	DROP DATABASE db_name;	DROP DATABASE db_name (CASCADE);

Current SQL Compatibility

Command Line

Function	Hive
Run Query	hive -e 'select a.col from tab1 a'
Run Query Silent Mode	hive -S -e 'select a.col from tab1 a'
Set Hive Config Variables	hive -e 'select a.col from tab1 a' -hiveconf hive.root.logger=DEBUG,console
Use Initialization Script	hive -i initialize.sql
Run Non-Interactive Script	hive -f script.sql