Hive supports subqueries in FROM clauses and WHERE clauses that you can use for many Apache Hive operations, such as filtering data from one table based on contents of another table. A subquery is a SQL expression in an inner query that returns a result set to the outer query. From the result set, the outer query is evaluated.
How do I use subqueries in hive?
Hive supports subqueries only in the FROM clause (through Hive 0.12). The subquery has to be given a name because every table in a FROM clause must have a name. Columns in the subquery select list must have unique names. The columns in the subquery select list are available in the outer query just like columns of a table.
How to write a sub query with equals clause in hive?
> hive does not support sub query with equals clause, you can write sub query only for IN, NOT IN, EXISTS and NOT EXISTS clause. > You cannot have a sub query which returns more than one row. Please look into - [https://cwiki.apache.org/confluence/display/Hive/Subqueries+in+SELECT][1]
Can I use subqueries in the FROM clause of a table?
Hive supports subqueries only in the FROM clause (through Hive 0.12). The subquery has to be given a name because every table in a FROM clause must have a name.
Does Apache Hive support inline correlated queries?
As of current version Apache Hive doesn’t support the inline correlated queries, that is, query written in an SELECT clause of parent or outer query. Note that, Apache Hive community is actively working on adding this feature.
Is subquery allowed in hive?
Hive supports subqueries only in the FROM clause (through Hive 0.12). The subquery has to be given a name because every table in a FROM clause must have a name. Columns in the subquery select list must have unique names.
How do I write subquery in select statement in hive?
How to write subquery in select statement in hiveIs what I want select foo1, foo2, foo3 from foos;Is what I will execute select foo1, foo2, foo3_input from foos;for each foo3 in a row I would like to execute the following query. foo3 = select bar1 from bars where (foo3_input) between val1 and val2;
Does Hive support correlated subquery?
ToDate inside of the subquery since hive does not support correlated sub queries.
Is it better to use subqueries instead of join?
The retrieval time of the query using joins almost always will be faster than that of a subquery. By using joins, you can maximize the calculation burden on the database i.e., instead of multiple queries using one join query.
Does Hive support with clause?
With the Help of Hive WITH clause you can reuse piece of query result in same query construct. You can also improve the Hadoop Hive query using WITH clause. You can simplify the query by moving complex, complicated repetitive code to the WITH clause and refer the logical table created in your SELECT statements.
How do I join two big tables in Hive?
If the tables don't meet the conditions, Hive will simply perform the normal Inner Join. If both tables have the same amount of buckets and the data is sorted by the bucket keys, Hive can perform the faster Sort-Merge Join. To activate it, you have to execute the following commands: set hive.
What queries are not supported in Hive?
Conversion of data to char type is not supported in Hive. Many organizations write custom user-defined Functions for these type of functions. You can create UDF in language of your choice.
What are the restriction of sub query in SQL Server?
A subquery can be nested inside the WHERE or HAVING clause of an outer SELECT , INSERT , UPDATE , or DELETE statement, or inside another subquery. Up to 32 levels of nesting is possible, although the limit varies based on available memory and the complexity of other expressions in the query.
What is Hive architecture?
Architecture of Hive Hive is a data warehouse infrastructure software that can create interaction between user and HDFS. The user interfaces that Hive supports are Hive Web UI, Hive command line, and Hive HD Insight (In Windows server).
Which is faster CTE or subquery?
Advantage of Using CTE CTE can be more readable: Another advantage of CTE is CTE are more readable than Subqueries. Since CTE can be reusable, you can write less code using CTE than using subquery. Also, people tend to follow the logic and ideas easier in sequence than in a nested fashion.
Are subqueries slower?
For multiple-table subqueries, execution of NULL IN (SELECT ...) is particularly slow because the join optimizer does not optimize for the case where the outer expression is NULL .
Which is faster subquery or correlated subquery?
Speed and Performance A correlated subquery is much slower than a non-correlated subquery because in the former, the inner query executes for each row of the outer query. This means if your table has n rows then whole processing will take the n * n = n^2 time, as compared to 2n times taken by a non-correlated subquery.
How do I exclude one column from select in Hive?
Add below properties to your 'hive-site. xml' file or execute it on the Hive interactive shell. Now, execute Hive query with a partition column that you want to exclude. For example, let us say you want to exclude date_col column from a query, execute something like below.
How can I retrieve multiple values in SQL?
The IN operator allows you to specify multiple values in a WHERE clause. The IN operator is a shorthand for multiple OR conditions.
How do I limit rows in Hive?
The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must both be non-negative integer constants. The first argument specifies the offset of the first row to return (as of Hive 2.0.
What is distribute by in Hive?
Syntax of Cluster By and Distribute By Hive uses the columns in Distribute By to distribute the rows among reducers. All rows with the same Distribute By columns will go to the same reducer. However, Distribute By does not guarantee clustering or sorting properties on the distributed keys.
What happens if the ON clause matches zero records in the right table?
If ON Clause matches zero records in the right table, the joins still return a record in the result with NULL in each column from the right table
What is a hive script?
Hive provides feasibility of writing user specific scripts for the client requirements. The users can able to write their own map and reduce scripts for the requirements. These are called Embedded Custom scripts . The coding logic is defined in the custom scripts and we can use that script in the ETL time.
What clause does hive use?
For this in Hive it uses TRANSFORM clause to embedded both map and reducer scripts.
What is a sub query?
A Query present within a Query is known as a sub query. The main query will depend on the values returned by the subqueries.
What is a right outer join in hive?
Hive query language RIGHT OUTER JOIN returns all the rows from the Right table even though there are no matches in left table
What does RIGHT join do?
RIGHT joins always return records from a Right table and matched records from the left table. If the left table is having no values corresponding to the column, it will return NULL values in that place.
Why do left, right, and full outer joins exist?
LEFT, RIGHT, FULL OUTER joins exist in order to provide more control over ON Clause for which there is no match
What is a correlated query in Apache Hive?
Apache Hive Correlated subquery is a query within a query that refer the columns from the outer query. Hive does support some of subqueris such as table subquery, WHERE clause subquery etc, and correlated subqueries. In most cases, the Hive correlated subqueries are used to improve the Hive query performance.
Does Hive support correlated subqueries?
These types of correlated subqueries are supported in database like Oracle. However, Hive does not support as of current version.
Does Apache Hive support inline correlated queries?
As of current version Apache Hive doesn’t support the inline correlated queries, that is, query written in an SELECT clause of parent or outer query. Note that, Apache Hive community is actively working on adding this feature. This feature may avaiable in future release.
Can you correlate queries in aggregations with group by and having clauses?
You cannot correlate the queries in aggregations with GROUP By and HAVING clauses
What is a subquery in SQL?
By definition, a subquery is a query nested inside another query such as SELECT, INSERT, UPDATE, or DELETE statement. In this tutorial, we are focusing on the subquery used with the SELECT statement.
What is the name of the query placed within parentheses?
Code language: SQL (Structured Query Language) (sql) The query placed within the parentheses is called a subquery. It is also known as an inner query or inner select. The query that contains the subquery is called an outer query or an outer select.
What does the exist operator do in SQL?
The EXISTS operator checks for the existence of rows returned from the subquery. It returns true if the subquery contains any rows. Otherwise, it returns false.
Where can a subquery be used in SQL?
SQL Subquery in the SELECT clause. A subquery can be used anywhere an expression can be used in the SELECT clause. The following example finds the salaries of all employees, their average salary, and the difference between the salary of each employee and the average salary.
Why is the table alias mandatory?
In this syntax, the table alias is mandatory because all tables in the FROM clause must have a name.
Why is it difficult to get a list of departments?
Because of the small data volume, you can get a list of department easily. However, in the real system with high volume data, it might be problematic. Another problem was that you have to revise the queries whenever you want to find employees who locate in a different location.
Is "some" a synonym for "any"?
Note that the SOME operator is a synonym for the ANY operator so you can use them interchangeably.
What is an uncorrelated subquery?
Those are queries where the result of the query can be treated as a constant for IN and NOT IN statements (called uncorrelated subqueries because the subquery does not reference columns from the parent query): The other supported types are EXISTS and NOT EXISTS subqueries:
Why does a subquery have to have a name?
The subquery has to be given a name because every table in a FROM clause must have a name. Columns in the subquery select list must have unique names. The columns in the subquery select list are available in the outer query just like columns of a table. The subquery can also be a query expression with UNION.
Does hive support subqueries?
Hive supports subqueries only in the FROM clause (through Hive 0.12). The subquery has to be given a name because every table in a FROM clause must have a name. Columns in the subquery select list must have unique names. The columns in the subquery select list are available in the outer query just like columns of a table. The subquery can also be a query expression with UNION. Hive supports arbitrary levels of subqueries.
Which side of expression is supported by subqueries?
These subqueries are only supported on the right-hand side of an expression.
