Question: What Is Temporary Table In Hive?

What is JSON MySQL?

MySQL supports a native JSON data type defined by RFC 7159 that enables efficient access to data in JSON (JavaScript Object Notation) documents.

JSON documents stored in JSON columns are converted to an internal format that permits quick read access to document elements..

Can you use a CTE in a stored procedure?

According to the CTE documentation, Common Table Expression is a temporary result set or a table in which we can do CREATE, UPDATE, DELETE but only within that scope. That is, if we create the CTE in a Stored Procedure, we can’t use it in another Stored Procedure.

Which is better CTE or temp table?

If you are joining multiple tables with millions of rows of records in each, CTE will perform significantly worse than temporary tables. Temp tables are always on disk – so as long as your CTE can be held in memory, it would most likely be faster (like a table variable, too).

What are Hive external tables?

External tables are tables where Hive has loose coupling with the data. All the write operations to the Managed tables are performed using Hive SQL commands. If a Managed table or partition is dropped, the data and metadata associated with that table or partition are deleted.

What is the difference between a temporary and variable table?

Temporary Tables are physically created in the tempdb database. These tables act as the normal table and also can have constraints, index like normal tables. Table Variable acts like a variable and exists for a particular batch of query execution. … It is created in the memory database but may be pushed out to tempdb.

Is CTE a temp table?

CTE stands for Common Table Expressions. It was introduced with SQL Server 2005. It is a temporary result set and typically it may be a result of complex sub-query. Unlike the temporary table, its life is limited to the current query.

How do you create a temporary table?

We go to “Object Explorer -> Databases -> System Databases-> tempdb -> Temporary Tables”. You must be wondering about the “000000000006” at the end of the table name. It is a unique identifier. Multiple database connections can create temporary tables with the same name.

How can you list all columns for a given table?

In a query editor, if you highlight the text of table name (ex dbo. MyTable) and hit ALT + F1 , you’ll get a list of column names, type, length, etc.

Why drop table if exists?

The DROP TABLE SQL statement enables you to delete a table from the database. If the table did not exist then attempting to DROP it would cause an error to occur. The DROP TABLE IF EXISTS SQL statement enables a check to see that the table exists prior to attempting the dropping (deletion) of the table.

How do I get the hive timestamp?

Hadoop Hive Date Functions ExamplesGet current date and timestamp using HiveQL. … Add 1 day to current date using HiveQL hive> select date_add(current_date(), 1); OK 2017-10-02 Time taken: 0.123 seconds, Fetched: 1 row(s)More items…•

What is a temporary table in MySQL?

In MySQL, a temporary table is a special type of table that allows you to store a temporary result set, which you can reuse several times in a single session. A temporary table is very handy when it is impossible or expensive to query data that requires a single SELECT statement with the JOIN clauses.

Are temp tables automatically dropped?

Temp tables are automatically dropped as soon as they go out of scope (the proc that they were created in completes) or the connection that created them closes.

Does MySQL 5.6 support JSON?

In MySQL 5.6, by default JSON_EXTRACT is not available by default. If you still need to access json data in MySQL 5.6, you need to write custom function.

Are CTEs faster than subqueries?

The performance of CTEs and subqueries should, in theory, be the same since both provide the same information to the query optimizer. One difference is that a CTE used more than once could be easily identified and calculated once. The results could then be stored and read multiple times.

Is there any dummy table in hive?

The dual table has one column, DUMMY, defined to be VARCHAR2(1) or CHAR(1), and contains one row with a value X. Selecting from the DUAL table is useful for computing a constant expression with the SELECT statement or evaluating user defined functions.

What is a drawback of JSON columns?

The other major drawback is with performance of json columns. They are likely to always be slower than native datatype in 99% of circumstances but can be optimized with indexes on virtual columns. The query syntax is also a little bit more complex.