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Answer: Execute the `ALTER TABLE ADD COLUMNS` command to add the new column, specifying a default value, and use the `GENERATED ALWAYS AS` clause to define it as a generated column.
The correct answer is A. The `ALTER TABLE ADD COLUMNS` command is the most efficient way to add a generated column to an existing Delta Lake table. By specifying the column with the `GENERATED ALWAYS AS` clause, you ensure that the column's values are computed based on other columns in the table, which optimizes storage and performance. This approach also allows you to set a default value for existing rows, fulfilling all the given requirements without the need for data migration or additional update operations.
Author: LeetQuiz Editorial Team
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In the context of managing a Delta Lake table within a Databricks environment, you are tasked with adding a new column that should automatically compute its values based on other columns in the table. This column must also have a default value for existing rows. Considering the need for efficiency in storage and performance, which of the following approaches correctly implements a generated column with these requirements? Choose the best option.
A
Execute the ALTER TABLE ADD COLUMNS command to add the new column, specifying a default value, and use the GENERATED ALWAYS AS clause to define it as a generated column.
B
Create a new table with the CREATE TABLE command, including the generated column definition in the WITH clause, and then migrate all data from the old table to the new one.
C
First, update all existing rows in the table to set the value of the new column using the UPDATE command, then add the column as a generated column with the ALTER TABLE ADD COLUMNS command.
D
Use the MERGE command to insert or update rows with the new column values, followed by the ALTER TABLE ADD COLUMNS command to add the column as a generated column.
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