Create External Table Format Quiz and Flashcards

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Questions and Answers

What is the purpose of the `CREATE EXTERNAL DATA SOURCE` statement in the provided text?

To define a connection to a Hadoop cluster (correct)

To define a connection to a SQL Server database

To define a connection to an Azure Blob Storage account

To define a connection to an Amazon S3 bucket

What is the purpose of the `CREATE EXTERNAL FILE FORMAT` statement in the provided text?

To define the format of data files in a SQL Server database

To define the format of data files in an Amazon S3 bucket

To define the format of data files in an Azure Blob Storage account

To define the format of data files in a Hadoop cluster (correct)

What is the purpose of the `CREATE EXTERNAL TABLE` statement in the provided text?

To create a table in a SQL Server database

To create a table in an Azure Blob Storage account

To create a table in an Amazon S3 bucket

To create a table in a Hadoop cluster (correct)

What is the purpose of the `CREATE DATABASE SCOPED CREDENTIAL` statement in the provided text?

To create a credential for accessing a SQL Server database Signup and view all the answers

What is the purpose of the `CREATE MASTER KEY` statement in the provided text?

To create a master key for encrypting data in a SQL Server database Signup and view all the answers

What is the purpose of the `SELECT INTO` statement in the provided text?

To create a new SQL Server table from the results of a query Signup and view all the answers

What is the purpose of the `JOIN` statement in the provided text?

To join data from a Hadoop cluster with data from a SQL Server database Signup and view all the answers

What is the purpose of the `PUSHDOWN` option in the `CREATE EXTERNAL DATA SOURCE` statement?

To enable push-down of predicates and aggregations to the Hadoop cluster Signup and view all the answers

What is the purpose of the `LOCATION` parameter in the `CREATE EXTERNAL DATA SOURCE` statement?

To specify the location of the Hadoop cluster Signup and view all the answers

What is the purpose of the `CREDENTIAL` parameter in the `CREATE EXTERNAL DATA SOURCE` statement?

To specify the credentials for accessing the SQL Server database Signup and view all the answers

What does SQL store for an external table?

Only the table metadata Signup and view all the answers

Why is it recommended to provide a three-part name for an external table?

For best performance Signup and view all the answers

What happens if the column definitions in an external table don't match the data in the external files?

File rows will be rejected Signup and view all the answers

In PolyBase, what happens when a query selects from an external table with a specified folder location?

Files are retrieved from the folder and subfolders Signup and view all the answers

What does PolyBase not return when querying from an external table?

.hidden files Signup and view all the answers

Where is the core-site.xml configuration file located for changing PolyBase settings?

\PolyBase\Hadoop\Conf\bin root of SQL Server Signup and view all the answers

Which clause defines the external data source (a shard map) that is used for the external table?

DATA_SOURCE Signup and view all the answers

Which data distribution method indicates that an application-specific method is used to distribute the data?

ROUND_ROBIN Signup and view all the answers

Which data type is not supported for columns in external tables for Azure SQL Database?

text Signup and view all the answers

What is the purpose of the SCHEMA_NAME and OBJECT_NAME clauses?

To map the external table definition to a table in a different schema Signup and view all the answers

Which data distribution method specifies that identical copies of the table are present on each database?

REPLICATED Signup and view all the answers

What is the purpose of the DISTRIBUTION clause in the CREATE EXTERNAL TABLE statement?

To specify the data distribution method Signup and view all the answers

What happens if the column definitions, including the data types and number of columns, do not match the data in the external files?

The file rows will be rejected when querying the actual data Signup and view all the answers

Which data distribution method specifies that the data from different tables don't overlap?

SHARDED Signup and view all the answers

Which clause allows you to configure column name, data type, nullability, and collation for an external table?

[ ,...n ] Signup and view all the answers

Which of the following is true about the DEFAULT CONSTRAINT on external tables in Azure SQL Database?

You can't use the DEFAULT CONSTRAINT on external tables Signup and view all the answers

What is the purpose of using GRANT or REVOKE statements for external tables?

To control access privileges to the external data source Signup and view all the answers

How does SQL Database handle data retrieval from an external data source in an ad hoc query scenario?

It creates a temporary table to store the retrieved data during query execution Signup and view all the answers

What happens to the temporary table created during an ad hoc query against an external table?

It is automatically dropped after the query completes Signup and view all the answers

In the import scenario, where does SQL Database store the data retrieved from an external data source?

In a permanent SQL table created during query execution Signup and view all the answers

What is a limitation of querying external tables compared to querying regular SQL Server tables?

Queries against external tables do not adhere to isolation semantics Signup and view all the answers

Which Data Definition Language (DDL) statements are allowed on external tables?

CREATE TABLE, DROP TABLE, CREATE VIEW, DROP VIEW Signup and view all the answers

Which of the following is the correct syntax for creating a master key in SQL Server?

CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'password'; Signup and view all the answers

What is the purpose of creating a database scoped credential in SQL Server?

To grant access to external data sources Signup and view all the answers

Which of the following is the correct syntax for creating an external data source in SQL Server?

CREATE EXTERNAL DATA SOURCE source_name WITH (LOCATION = 'oracle://[:]', CREDENTIAL = credential_name); Signup and view all the answers

What is the purpose of the `PUSHDOWN` option when creating an external data source in SQL Server?

To enable or disable query pushdown optimization Signup and view all the answers

Which of the following is the correct syntax for creating an external table in SQL Server for Oracle?

CREATE EXTERNAL TABLE customers(...) WITH (LOCATION = 'DB1.mySchema.customer', DATA_SOURCE = external_data_source_name); Signup and view all the answers

What is the purpose of the `LOCATION` option when creating an external table in SQL Server?

To specify the location or path of the external data Signup and view all the answers

Which of the following is the correct syntax for creating an external file format in SQL Server for Parquet files?

CREATE EXTERNAL FILE FORMAT ParquetFileFormat WITH (FORMAT_TYPE = PARQUET); Signup and view all the answers

What is the purpose of the `FILE_FORMAT` option when creating an external table in SQL Server?

To specify the file format of the external data Signup and view all the answers

Which of the following is the correct syntax for querying a Parquet file stored in S3-compatible object storage via an external table in SQL Server?

SELECT * FROM Region; Signup and view all the answers

What is the purpose of the `sp_data_source_objects` system stored procedure in SQL Server?

To retrieve metadata about external data sources and external tables Signup and view all the answers

What is the purpose of the matching suffix for corresponding data and reason files?

To ensure the files are related and can be easily identified Signup and view all the answers

Which of the following permissions is not required to create an external table in SQL Server?

CREATE TABLE Signup and view all the answers

What is the purpose of the `DATABASE SCOPED CREDENTIAL` used in the `CREATE EXTERNAL TABLE` command?

To provide authentication credentials for the external data source Signup and view all the answers

When using an external table to export data to a Hadoop or Azure Storage external data source, what additional permission is required for the login specified in the `DATABASE SCOPED CREDENTIAL`?

WRITE Signup and view all the answers

What is the purpose of the `ALTER ANY EXTERNAL DATA SOURCE` permission?

Both a and b Signup and view all the answers

What happens if the attempt to connect to the external data source fails when executing the `CREATE EXTERNAL TABLE` statement?

The statement will fail, and the external table won't be created Signup and view all the answers

What is the difference between ad hoc query scenarios and import scenarios when using an external table in SQL Server?

In ad hoc queries, PolyBase stores the retrieved rows in a temporary table, while in import scenarios the new table is created during query execution Signup and view all the answers

What is the purpose of the `Hadoop resource manager location` option in the `CREATE EXTERNAL DATA SOURCE` statement?

To enable predicate pushdown to improve query performance Signup and view all the answers

What is a limitation of using external tables in SQL Server?

Query results against an external table are not guaranteed to be deterministic Signup and view all the answers

What is the restriction on simultaneously running queries against different Hadoop data sources in SQL Server?

The queries must use the same Hadoop connectivity server configuration setting Signup and view all the answers

What is the purpose of the REJECT_TYPE option in PolyBase?

To specify whether the REJECT_VALUE option is a literal value or a percentage Signup and view all the answers

What is the purpose of the REJECT_VALUE option in PolyBase?

To specify the value or the percentage of rows that can be rejected before the query fails Signup and view all the answers

What is the purpose of the REJECT_SAMPLE_VALUE option in PolyBase?

To determine the number of rows to attempt to retrieve before PolyBase recalculates the percentage of rejected rows Signup and view all the answers

What happens when the percentage of rejected rows exceeds the REJECT_VALUE in PolyBase?

The query will return partial results until the reject threshold is exceeded, then fail with an error message Signup and view all the answers

What is the purpose of the REJECTED_ROW_LOCATION option in PolyBase?

To specify the directory within the External Data Source where the rejected rows and error files should be written Signup and view all the answers

What is the format of the directory created for the rejected rows and error files in PolyBase?

The directory is named based on the time of load submission in the format YearMonthDay-HourMinuteSecond Signup and view all the answers

What is the purpose of the "_" character in the REJECTED_ROW_LOCATION directory name?

To ensure the directory is escaped for other data processing Signup and view all the answers

Which external data sources can use the REJECTED_ROW_LOCATION option in PolyBase?

Only external data sources where TYPE = HADOOP and for external tables using DELIMITEDTEXT FORMAT_TYPE Signup and view all the answers

What types of files are written in the REJECTED_ROW_LOCATION directory in PolyBase?

Both the rejected rows files and the error files Signup and view all the answers

How does PolyBase calculate the percentage of failed rows when using the REJECT_TYPE = percentage option?

PolyBase calculates the percentage of failed rows at intervals, after attempting to retrieve the number of rows specified by the REJECT_SAMPLE_VALUE option Signup and view all the answers

What happens if the percentage of failed rows exceeds the REJECT_VALUE when using the REJECT_TYPE = percentage option in PolyBase?

The query will return partial results until the reject threshold is exceeded, then fail with an error message Signup and view all the answers

What is the primary purpose of creating an external table using the CREATE EXTERNAL TABLE command?

To provide access to data stored in a Hadoop cluster or Azure Blob Storage Signup and view all the answers

Which of the following is a primary use case for external data sources when used with an external table?

Data virtualization and data load using PolyBase Signup and view all the answers

What is the minimum version of SQL Server required to use the CREATE EXTERNAL TABLE command?

SQL Server 2016 Signup and view all the answers

Which of the following statements is true about the syntax conventions used in the CREATE EXTERNAL TABLE command?

The syntax conventions are specific to Transact-SQL Signup and view all the answers

Which of the following is a secondary use case for external data sources when used with an external table?

Bulk load operations using SQL Server or SQL Database using BULK INSERT or OPENROWSET Signup and view all the answers

What is the primary purpose of the DROP EXTERNAL TABLE command mentioned in the text?

To remove the external table definition from the SQL Server database Signup and view all the answers

Which of the following statements is NOT allowed on external tables in PolyBase?

INSERT Signup and view all the answers

What is the maximum number of files PolyBase can consume per folder when running 32 concurrent queries?

33k files Signup and view all the answers

Which of the following data types CANNOT be used in PolyBase external tables?

Both geography and text Signup and view all the answers

What is the row width limit for PolyBase in SQL Server 2016?

32 KB Signup and view all the answers

Which of the following statements is true about creating external tables to MongoDB collections that contain arrays?

Both of the above approaches are valid Signup and view all the answers

What type of lock is acquired on the `SCHEMARESOLUTION` object when working with PolyBase external tables?

Shared lock Signup and view all the answers

Which of the following statements is true about the security of data files for an external table in PolyBase?

It is your responsibility to manage the security of the external data files Signup and view all the answers

In the provided example for creating an external table with data in text-delimited format, what is the value of the `FIELD_TERMINATOR` option in the `myfileformat` external file format?

'|' Signup and view all the answers

Which of the following statements is true about the `LOCATION` option when creating an external table in PolyBase?

It specifies the path to the external data files Signup and view all the answers

In the provided example for creating an external table with data in RCFile format, what is the value of the `FORMAT_TYPE` option in the `myfileformat_rc` external file format?

RCFILE Signup and view all the answers

Study Notes

External Data Sources and Tables

CREATE EXTERNAL DATA SOURCE statement creates a reference to an external data source.
CREATE EXTERNAL FILE FORMAT statement defines the format of an external file.
CREATE EXTERNAL TABLE statement creates an external table, which is a virtual table that references data in an external data source.

Security and Authentication

CREATE DATABASE SCOPED CREDENTIAL statement creates a credential that can be used to authenticate to an external data source.
CREATE MASTER KEY statement creates a master key, which is used to encrypt the credential.
CREDENTIAL parameter in CREATE EXTERNAL DATA SOURCE statement specifies the credential to use for authentication.

External Tables

External tables store metadata about the external data, not the data itself.
Providing a three-part name for an external table is recommended for clarity and unambiguity.
If column definitions in an external table don't match the data in the external files, the query will fail.
PolyBase returns only the rows that match the specified folder location when querying an external table.

Querying External Tables

SELECT INTO statement is used to import data from an external table into a regular SQL Server table.
JOIN statement can be used to combine data from an external table with data from a regular SQL Server table.
PolyBase does not return data that is not present in the external files when querying an external table.

PolyBase Settings

The core-site.xml configuration file is used to change PolyBase settings.
The PUSHDOWN option in CREATE EXTERNAL DATA SOURCE statement enables pushdown operations.
The LOCATION parameter in CREATE EXTERNAL DATA SOURCE statement specifies the location of the external data source.

Data Distribution

The DISTRIBUTION clause in CREATE EXTERNAL TABLE statement specifies how the data is distributed.
The SCHEMA_NAME and OBJECT_NAME clauses define the schema and name of the external table.
The REPLICATED distribution method specifies that identical copies of the table are present on each database.

Data Types and Constraints

The DEFAULT CONSTRAINT on external tables in Azure SQL Database is not supported.
The GRANT and REVOKE statements are used to manage permissions on external tables.
External tables have limitations compared to regular SQL Server tables, such as data type restrictions.

Ad Hoc Queries and Import Scenarios

In ad hoc query scenarios, SQL Database stores the data in a temporary table.
In import scenarios, SQL Database stores the data in a regular SQL Server table.

Creating External Tables

The correct syntax for creating an external table in SQL Server for Oracle is CREATE EXTERNAL TABLE ... FOR Oracle.
The LOCATION option specifies the location of the external table.
The FILE_FORMAT option specifies the format of the external files.