Undrop for recovering dropped objects in Snowflake - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the UNDROP command do in Snowflake?

The UNDROP command recovers a dropped object, such as a table or schema, restoring it to its state before deletion.

beginner

Which types of objects can you recover using UNDROP in Snowflake?

You can recover tables, schemas, and databases that were dropped, as long as they are within the retention period.

intermediate

What is the retention period for dropped objects in Snowflake before they are permanently deleted?

Dropped objects are retained for a default period of 1 day (24 hours), but this can be extended up to 90 days depending on account settings.

intermediate

How do you find the name of a dropped object to use with UNDROP?

You can use the SHOW <object_type> HISTORY command (where <object_type> is TABLES, SCHEMAS, or DATABASES) to see recently dropped objects and their names.

beginner

What happens if you try to UNDROP an object that no longer exists in the dropped objects list?

The UNDROP command will fail because the object is permanently deleted and cannot be recovered.

What is the main purpose of the UNDROP command in Snowflake?

A To recover a dropped object

B To permanently delete an object

C To rename an object

D To create a new object

UNDROP is used to recover objects that were dropped, restoring them to their previous state.

Which of the following helps you find recently dropped objects in Snowflake?

A INFORMATION_SCHEMA.SCHEMATA

B INFORMATION_SCHEMA.TABLES

C INFORMATION_SCHEMA.COLUMNS

D SHOW TABLES HISTORY

The SHOW TABLES HISTORY command lists objects that were recently dropped and can be recovered.

How long is the default retention period for dropped objects in Snowflake?

A 90 days

B 7 days

C 24 hours

D 30 days

By default, dropped objects are kept for 24 hours before permanent deletion, but this can be extended up to 90 days depending on account settings.

What happens if you try to UNDROP an object after the retention period has expired?

A The command fails because the object is permanently deleted

B The object is recovered anyway

C The object is renamed

D The retention period is extended automatically

Once the retention period expires, the object is permanently deleted and cannot be recovered.

Which of these objects can you NOT recover with UNDROP?

A A dropped table

B A dropped file in external storage

C A dropped database

D A dropped schema

UNDROP only works for Snowflake objects like tables, schemas, and databases, not external files.

Explain how to recover a dropped table in Snowflake using the UNDROP command.

Think about how to find the dropped object and the command syntax.

Describe the retention period concept for dropped objects in Snowflake and its importance.

Consider why Snowflake keeps dropped objects temporarily.

Practice

1. What is the primary purpose of the UNDROP command in Snowflake?

easy

A. To recover a dropped table, view, or schema within the retention period

B. To permanently delete a table or schema from Snowflake

C. To create a new table with the same structure as an existing one

D. To rename an existing table or schema

Solution

1. Step 1: Understand the function of UNDROP

   The UNDROP command is designed to restore objects that were accidentally dropped, such as tables, views, or schemas.

2. Step 2: Identify the correct use case

   Since UNDROP recovers dropped objects within the retention period, it is not used for deletion, creation, or renaming.

3. Final Answer:

   To recover a dropped table, view, or schema within the retention period -> Option A

4. Quick Check:

   UNDROP = Recover dropped objects [OK]

Hint: UNDROP means undo drop to restore deleted objects [OK]

Common Mistakes:

• Confusing UNDROP with DELETE or DROP commands
• Thinking UNDROP creates new objects
• Assuming UNDROP renames objects

2. Which of the following is the correct syntax to undrop a table named sales_data in Snowflake?

easy

A. UNDROP TABLE sales_data;

B. RECOVER TABLE sales_data;

C. UNDROP TABLE IF EXISTS sales_data;

D. RESTORE TABLE sales_data;

Solution

1. Step 1: Recall the correct UNDROP syntax

   The correct syntax to recover a dropped table is UNDROP TABLE <table_name>;

2. Step 2: Eliminate incorrect options

   Adding IF EXISTS is invalid with UNDROP. RECOVER and RESTORE are not supported commands for recovering dropped tables in Snowflake.

3. Final Answer:

   UNDROP TABLE sales_data; -> Option A

4. Quick Check:

   UNDROP TABLE = correct syntax [OK]

Hint: Use UNDROP TABLE followed by the table name [OK]

Common Mistakes:

• Using RECOVER or RESTORE instead of UNDROP
• Adding IF EXISTS which is invalid with UNDROP
• Missing the TABLE keyword

3. Consider the following sequence of commands in Snowflake:

DROP TABLE IF EXISTS customers;
UNDROP TABLE customers;

What will be the result of the UNDROP TABLE customers; command assuming the drop happened within the retention period?

medium

A. An error will occur because the table does not exist

B. The command will be ignored silently

C. The table will be restored but without any data

D. The table 'customers' will be restored with its data intact

Solution

1. Step 1: Understand the effect of DROP and UNDROP

   The DROP TABLE command deletes the table but keeps it recoverable within the retention period. UNDROP restores the dropped table with its data.

2. Step 2: Confirm retention period and command behavior

   Since the drop is recent and within retention, UNDROP will successfully restore the table and its data.

3. Final Answer:

   The table 'customers' will be restored with its data intact -> Option D

4. Quick Check:

   UNDROP restores dropped table and data [OK]

Hint: UNDROP restores table and data if within retention [OK]

Common Mistakes:

• Assuming UNDROP only restores structure, not data
• Thinking UNDROP fails if table was dropped
• Believing UNDROP silently ignores missing tables

4. You tried to undrop a dropped schema using UNDROP SCHEMA sales_schema; but received an error. Which of the following is the most likely cause?

medium

A. You used the wrong command; UNDROP does not support schemas

B. The schema was dropped outside the retention period

C. The schema name is case-sensitive and was typed incorrectly

D. You need to run UNDROP with the database name specified

Solution

1. Step 1: Check retention period requirement

   UNDROP only works if the object was dropped within the retention period. If dropped too long ago, recovery fails.

2. Step 2: Verify command support and syntax

   UNDROP supports schemas, and schema names are case-insensitive by default. Database name is not required if context is set.

3. Final Answer:

   The schema was dropped outside the retention period -> Option B

4. Quick Check:

   Retention period exceeded causes UNDROP error [OK]

Hint: Check retention period before undropping schemas [OK]

Common Mistakes:

• Assuming UNDROP can't recover schemas
• Ignoring retention period limits
• Mistyping schema name without checking case sensitivity

5. You accidentally dropped a table orders in your production database. You want to recover it using UNDROP, but you also want to ensure no data loss and minimal downtime. Which of the following steps is the best approach?

hard

A. Wait for the retention period to expire and then restore from a full database backup

B. Recreate the table manually and import data from backups

C. Immediately run UNDROP TABLE orders; within the retention period and verify data integrity

D. Use UNDROP TABLE orders; only after recreating the table structure

Solution

1. Step 1: Use UNDROP immediately after accidental drop

   UNDROP recovers the dropped table with data if done within the retention period, minimizing downtime and data loss.

2. Step 2: Avoid manual recreation or waiting unnecessarily

   Manual recreation or waiting for backup restore increases downtime and risks data loss.

3. Final Answer:

   Immediately run UNDROP TABLE orders; within the retention period and verify data integrity -> Option C

4. Quick Check:

   UNDROP quickly recovers dropped tables with data [OK]

Hint: Run UNDROP immediately after drop to avoid data loss [OK]

Common Mistakes:

• Delaying UNDROP beyond retention period
• Recreating table manually before undropping
• Ignoring data verification after recovery