Udemy Data Lake Quiz: Understanding Delta Tables and Creating a Delta Lake Table

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Questions and Answers

What is the default format of the table created in Delta Lake?

CSV

JSON

Parquet

Delta (correct)

What command is used to explore table metadata in Delta Lake?

SHOW TABLE

DESCRIBE

DESCRIBE DETAIL (correct)

DESCRIBE FORMATTED

What information can be seen in the table metadata in Delta Lake?

Only the location of the table

The table schema, location, and number of files (correct)

The table schema, location, and query history

Only the table schema

What is the purpose of the 'USING DELTA' keyword in Delta Lake?

It is not used in Delta Lake Signup and view all the answers

Why does Spark create four files for a single insert operation?

Because the cluster has four cores, and each core executes one file Signup and view all the answers

What happens to the original files when an update operation is performed on a Delta table?

They are left unchanged, and new files are added with the updated data Signup and view all the answers

What is the purpose of the transaction log in Delta Lake?

To store the history of operations on the table Signup and view all the answers

How many versions of the table are stored in the transaction log?

Three, representing the initial creation, insert, and update operations Signup and view all the answers

What is stored in the _delta_log folder in the table directory?

The transaction log in JSON format Signup and view all the answers

What information can be found in the JSON files in the _delta_log folder?

The list of files added and removed from the table Signup and view all the answers

What is the main reason why the update operation resulted in two new files being added to the directory?

Because the Delta Lake table uses a parallel processing approach Signup and view all the answers

What is the primary function of the transaction log in Delta Lake?

To store the history of all operations on the table Signup and view all the answers

What happens to the files that are no longer valid in the current version of the table?

They are soft deleted from the table Signup and view all the answers

What is the purpose of the DESCRIBE DETAIL command in Delta Lake?

To view the current version of the table Signup and view all the answers

What is stored in the JSON files in the _delta_log folder?

The transaction information, including adds and removes Signup and view all the answers

What is the main advantage of using Delta Lake's transaction log?

It provides a full history of all operations on the table Signup and view all the answers

What is the benefit of using the DESCRIBE DETAIL command in Delta Lake?

It provides information about the table metadata. Signup and view all the answers

What happens when we create a table in Delta Lake without specifying the USING DELTA keyword?

The table is created as a Delta Lake table by default. Signup and view all the answers

What is the benefit of using INSERT INTO statements in Delta Lake?

It allows us to insert multiple records into the table in a single transaction. Signup and view all the answers

What is the purpose of the table schema in Delta Lake?

It is used to define the structure of the table. Signup and view all the answers

What can be seen in the Location field of the table metadata in Delta Lake?

The location where the table files are stored. Signup and view all the answers

Study Notes

Creating a Delta Lake Table

A Delta Lake table is created using a CREATE TABLE statement with a table name and schema.
The table schema defines the columns and their data types, e.g., ID of type integer, Name of type String, and Salary of type double.
Delta Lake is the default format, so the USING DELTA keyword is not required.

Confirming Table Creation

The table is created in the default database.
The table schema can be viewed in the Data tab, including columns and metadata information.

Inserting Records

Records are inserted using an INSERT INTO statement.
Multiple records can be inserted in a single transaction.

Querying the Table

The table can be queried using a standard SELECT statement.

Table Metadata

The DESCRIBE DETAIL command provides metadata information about the table.
Metadata includes table location, number of files, and other information.
The table location is where the table files are stored.
The number of files indicates the number of data files in the current table version.

Exploring Table Files

The %fs Magic Command can be used to explore the table files.
The table directory contains data files in parquet format.
The number of files is determined by the number of parallel executors in the Spark cluster.

Update Operations

Update operations are performed using a UPDATE statement.
Updates create new files instead of modifying existing ones.
The transaction log is used to indicate which files are valid in the current version of the table.

Table History

The DESCRIBE HISTORY command provides a history of the table.
The transaction log stores all changes to the table, allowing for easy review of table history.
The transaction log is located in the _delta_log folder in the table directory.
Each transaction is a new JSON file written to the Delta Lake transaction log.

Transaction Log

The transaction log contains JSON files representing each transaction.
The JSON files contain information about the new files written to the table and the files that have been soft deleted.
The transaction log allows for easy tracking of changes to the table.

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Description

Learn how to create an empty Delta Lake table with a CREAT TABLE statement, specifying the table name and schema. The ID is of type integer, Name is a String, and Salary is a double.

Udemy 11. Understanding Delta Tables - Creating a Delta Lake Table

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