Hadoop Hive supports various join types. Objective.
A predicate that is in the JOIN ON clause.
Hive deals with two types of table structures like Internal and External tables depending on the loading and design of schema in Hive. So, when we perform a normal join, the job is sent to a Map-Reduce task which splits the main task into 2 stages – “Map stage” and “Reduce stage”. There are multiple ways to load data into Hive tables.
You may get the requirement to choose the joining values based on certain conditions. A JOIN condition is to be raised using the primary keys and foreign keys of the tables.
For example, in 'R1 join R2 on R1.x = 5' the predicate 'R1.x = 5' is a During Join predicate.
As discussed the basics of Hive tables in Hive Data Models, let us now explore the major difference between hive internal and external tables. SQL SET Operator MINUS Alternative in Hive. In a similar line we’ve Hive Query Language(HQL or HiveQL) joins; which is the key factor for the optimization and performance of hive queries.
However, there are many more insights of Apache Hive Map join.
Its columns are the same as those in ALL_HIVE_TABLES. The joining condition can be on the common columns between participating tables.
Map join is a feature used in Hive queries to increase its efficiency in terms of speed.
2. An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them.
The MINUS operator finds the difference between two tables or sub-queries and return results from only first SELECT statement. In this article, we will check SQL set operator MINUS alternative in Hive with an example.
Coming to Tables it's just like the way that we create in traditional Relational Databases.
JOIN is same as OUTER JOIN in SQL. The functionalities such as filtering, joins can be performed on the tables. The user can create an external table that points to a specified location within HDFS . For full outer joins both tables are also Null Supplying tables. In this article, we are going to discuss the two different types of Hive Table that are Internal table (Managed table) and External table. The following query executes JOIN on the CUSTOMER and ORDER tables, and retrieves the records: hive> SELECT c.ID, c.NAME, c.AGE, o.AMOUNT > FROM CUSTOMERS c JOIN ORDERS o > ON (c.ID = o.CUSTOMER_ID); The primary purpose of defining an external table is to access and execute queries on data stored outside the Hive. Join is a condition used to combine the data from 2 tables. In Apache Hive, there is a feature that we use to speed up Hive queries.Basically, that feature is what we call Map join in Hive. Introduction to Map Join in Hive. In SQL, MINUS is also called EXCEPT. Curious to know different types of Hive tables and how they are different from each other? Fundamentally, there are two types of tables in HIVE – Managed or Internal tables and external tables. Map Join in Hive is also Called Map Side Join in Hive.
Introduction to Bucket Map Join. Requirement You have two tables named as A and B and you want to perform all types of join in Pig.
1. During Join predicate. In the non-full outer join case, this is the other table in the Join. In Apache Hive, while the tables are large and all the tables used in the join are bucketed on the join columns we use Hive Bucket Map Join feature.Moreover, one table should have buckets in multiples of the number of buckets in another table in this type of join. After Join predicate. Introduction to External Table in Hive. The join in Hive is used to combine the records from multiple tables based on the joining condition.
An external table is a table that describes the schema or metadata of external files.
In this particular usage, the user can copy a file into the specified location using the HDFS put or copy commands and create a table pointing to this location with all the relevant row format information. DBA_HIVE_TABLES provides information about all the Hive tables in the Hive metastore.