(Delta) Chapter 3: Basic Operations on Delta Tables
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Questions and Answers

The DeltaTableBuilder API is only used for loading data from a DataFrame.

False

The DROP TABLE IF EXISTS statement is used to create a new table.

False

The write method is used to save the DataFrame as a Delta table.

True

The SELECT * FROM taxidb.rateCard statement is used to create a Delta table.

<p>False</p> Signup and view all the answers

The DeltaTableBuilder API is designed to work with DataFrames.

<p>False</p> Signup and view all the answers

The mode('overwrite') option is used to append data to an existing table.

<p>False</p> Signup and view all the answers

The option('path', DELTALAKE_PATH) option is used to specify the column names.

<p>False</p> Signup and view all the answers

The Builder design pattern is only used in the DeltaTableBuilder API.

<p>False</p> Signup and view all the answers

The CREATE TABLE IF NOT EXISTS command is used to update an existing table.

<p>False</p> Signup and view all the answers

A catalog allows you to register a table with a file format and path notation.

<p>False</p> Signup and view all the answers

The Hive catalog is the least widely used catalog in the Spark ecosystem.

<p>False</p> Signup and view all the answers

You can use the standard SQL DDL commands in Spark SQL to create a Delta table.

<p>True</p> Signup and view all the answers

The LOCATION keyword is used to specify the database name.

<p>False</p> Signup and view all the answers

You can refer to a Delta table as delta./mnt/datalake/book/chapter03/rateCard after creating a database named taxtdb.

<p>False</p> Signup and view all the answers

The CREATE DATABASE IF NOT EXISTS command is used to create a new Delta table.

<p>False</p> Signup and view all the answers

The DESCRIBE command can be used to return the basic metadata for a CSV file.

<p>False</p> Signup and view all the answers

The python -m json.tool command is used to search for the string 'metadata' in the transaction log entry.

<p>False</p> Signup and view all the answers

The schema of the table is not written to the transaction log entry.

<p>False</p> Signup and view all the answers

The 'createdTime' field in the metadata contains the name of the provider.

<p>False</p> Signup and view all the answers

The DESCRIBE command is used to modify the metadata of a Delta table.

<p>False</p> Signup and view all the answers

The number of files created when partitioning by multiple columns is the sum of the cardinality of both columns.

<p>False</p> Signup and view all the answers

Z-ordering is a type of partitioning.

<p>False</p> Signup and view all the answers

The SELECT COUNT(*) &gt; 0 FROM statement is used to create a new partition.

<p>False</p> Signup and view all the answers

The 'small file problem' occurs when a small number of large Parquet part files are created.

<p>False</p> Signup and view all the answers

Partitioning by multiple columns is not supported.

<p>False</p> Signup and view all the answers

Partitioning by multiple columns always leads to the 'small file problem'.

<p>False</p> Signup and view all the answers

The DeltaTableBuilder API offers coarse-grained control when creating a Delta table.

<p>False</p> Signup and view all the answers

The DESCRIBE command can be used to modify the metadata of a Delta table.

<p>False</p> Signup and view all the answers

The schema of the table is stored in XML format and can be accessed using the grep command.

<p>False</p> Signup and view all the answers

Partitioning a Delta table always leads to the creation of a single file.

<p>False</p> Signup and view all the answers

The CREATE TABLE command is used to create a new Delta table.

<p>True</p> Signup and view all the answers

The 'small file problem' occurs when a large number of small Parquet part files are created.

<p>True</p> Signup and view all the answers

Z-ordering is a type of partitioning that can be used to alleviate the 'small file problem'.

<p>True</p> Signup and view all the answers

The number of files created when partitioning by multiple columns is the sum of the cardinality of both columns.

<p>False</p> Signup and view all the answers

Study Notes

Creating a Delta Table

  • A Delta table can be created using standard SQL DDL commands in Spark SQL.
  • The notation for creating a Delta table is CREATE TABLE ... USING DELTA LOCATION '/path/to/table'.
  • This notation can be tedious to use, especially when working with long filepaths.

Using Catalogs

  • Catalogs allow you to register a table with a database and table name notation, making it easier to refer to the table.
  • Creating a database and table using a catalog notation simplifies the process of creating a Delta table.
  • For example, creating a database named taxtdb and a table named rateCard using the catalog notation: CREATE TABLE taxtdb.rateCard (...) USING DELTA LOCATION '/mnt/datalake/book/chapter03/rateCard'.

Metadata and Schema

  • Delta Lake writes the schema of the table to the transaction log entry, along with auditing and partitioning information.
  • The schema is stored in JSON format and can be accessed using the grep command and python -m json.tool.

DESCRIBE Statement

  • The SQL DESCRIBE command can be used to return the basic metadata for a Parquet file or Delta table.
  • Dropping an existing table and recreating it with the DESCRIBE statement can be used to verify that the data has been loaded correctly.

Creating a Delta Table with the DeltaTableBuilder API

  • The DeltaTableBuilder API offers fine-grained control when creating a Delta table.
  • It allows users to specify additional information such as column comments, table properties, and generated columns.
  • The API is designed to work with Delta tables and offers more control than the traditional DataFrameWriter API.

Partitioning and Files

  • Partitioning a Delta table can lead to the creation of multiple files, which can lead to the "small file problem".
  • The number of files created is the product of the cardinality of both columns, which can lead to a large number of small Parquet part files.
  • Alternative solutions, such as Z-ordering, can be more effective than partitioning for certain use cases.

Checking if a Partition Exists

  • To check if a partition exists in a table, use the statement SELECT COUNT(*) &gt; 0 FROM ... WHERE ....
  • If the partition exists, the statement returns true.

Creating a Delta Table

  • A Delta table can be created using standard SQL DDL commands in Spark SQL.
  • The notation for creating a Delta table is CREATE TABLE...USING DELTA LOCATION '/path/to/table'.
  • Catalogs can be used to register a table with a database and table name notation, making it easier to refer to the table.

Metadata and Schema

  • Delta Lake writes the schema of the table to the transaction log entry.
  • The schema is stored in JSON format and can be accessed using the grep command and python -m json.tool.
  • Auditing and partitioning information are also stored in the transaction log entry.

DESCRIBE Statement

  • The SQL DESCRIBE command can be used to return the basic metadata for a Parquet file or Delta table.
  • The DESCRIBE statement can be used to verify that the data has been loaded correctly by dropping an existing table and recreating it.

DeltaTableBuilder API

  • The DeltaTableBuilder API offers fine-grained control when creating a Delta table.
  • The API allows users to specify additional information such as column comments, table properties, and generated columns.
  • The DeltaTableBuilder API is designed to work with Delta tables and offers more control than the traditional DataFrameWriter API.

Partitioning and Files

  • Partitioning a Delta table can lead to the creation of multiple files, which can lead to the "small file problem".
  • The number of files created is the product of the cardinality of both columns.
  • Alternative solutions, such as Z-ordering, can be more effective than partitioning for certain use cases.

Checking if a Partition Exists

  • To check if a partition exists in a table, use the statement SELECT COUNT(*) &gt; 0 FROM...WHERE....
  • If the partition exists, the statement returns true.

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(Delta) Ch 3 Basic Commands.pdf

Description

Learn about creating Delta tables in DataBricks, specifying paths and names. This quiz covers basic operations on Delta tables, including writing and formatting modes.

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