Why Time Travel enables data recovery in Snowflake - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to query data as it existed 1 hour ago using Time Travel.

Snowflake

SELECT * FROM sales_data AT (OFFSET => [1]);

Drag options to blanks, or click blank then click option'

A60

B3600

C1800

D7200

Attempts:

3 left

💡 Hint

Common Mistakes

Using minutes instead of seconds for OFFSET.

Using a negative number for OFFSET.

Time Travel in Snowflake allows querying data as it was in the past. The OFFSET value is in seconds, so 3600 seconds equals 1 hour ago.

2fill in blank

medium

Complete the code to restore a dropped table using Time Travel.

Snowflake

UNDROP TABLE [1];

Drag options to blanks, or click blank then click option'

Asales_data

Bcustomers

Corders

Dinventory

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to undrop a table that was never dropped.

Using a wrong table name.

The UNDROP command restores a dropped table. Here, 'sales_data' is the table to recover.

3fill in blank

hard

Fix the error in the query to select data from 2 hours ago using Time Travel.

Snowflake

SELECT * FROM orders AT (OFFSET => [1]);

Drag options to blanks, or click blank then click option'

A7200

B-7200

C120

D3600

Attempts:

3 left

💡 Hint

Common Mistakes

Using negative OFFSET value.

Using minutes instead of seconds.

The OFFSET value must be positive and represents seconds in the past. 2 hours = 7200 seconds.

4fill in blank

hard

Fill both blanks to query the 'customers' table as it was 30 minutes ago using Time Travel.

Snowflake

SELECT * FROM customers AT ([1] => [2]);

Drag options to blanks, or click blank then click option'

AOFFSET

BTIMESTAMP

C1800

D3600

Attempts:

3 left

💡 Hint

Common Mistakes

Using TIMESTAMP keyword with seconds value.

Using 3600 seconds for 30 minutes.

To query data 30 minutes ago, use OFFSET with 1800 seconds (30 × 60).

5fill in blank

hard

Fill all three blanks to restore the 'inventory' table dropped recently and query its state 15 minutes ago.

Snowflake

UNDROP TABLE [1]; SELECT * FROM [2] AT ([3] => 900);

Drag options to blanks, or click blank then click option'

Ainventory

Bsales_data

COFFSET

DTIMESTAMP

Attempts:

3 left

💡 Hint

Common Mistakes

Using different table names for undrop and select.

Using TIMESTAMP instead of OFFSET.

First, undrop the 'inventory' table, then query it 15 minutes ago using OFFSET with 900 seconds (15 × 60).

Practice

1. What is the main benefit of Snowflake's Time Travel feature?

easy

A. It automatically backs up data to an external system.

B. It speeds up query performance by caching results.

C. It encrypts data to enhance security.

D. It allows you to recover data from a previous point in time.

Solution

1. Step 1: Understand Time Travel purpose

   Time Travel lets you access data as it was at a past time, enabling recovery.

2. Step 2: Compare options

   Only recovering past data matches Time Travel's main benefit; others describe different features.

3. Final Answer:

   It allows you to recover data from a previous point in time. -> Option D

4. Quick Check:

   Time Travel = Data recovery [OK]

Hint: Time Travel means going back to old data states [OK]

Common Mistakes:

• Confusing Time Travel with backup or encryption
• Thinking it improves query speed
• Assuming it stores data outside Snowflake

2. Which SQL syntax correctly queries data from 2 hours ago using Time Travel?

easy

A. SELECT * FROM table BEFORE (TIMESTAMP => CURRENT_TIMESTAMP - INTERVAL '2' HOUR);

B. SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -2, CURRENT_TIMESTAMP));

C. SELECT * FROM table AT (OFFSET => -7200);

D. SELECT * FROM table FOR TIME TRAVEL 2 HOURS AGO;

Solution

1. Step 1: Recall correct Time Travel syntax

   Snowflake uses AT (TIMESTAMP => ...) to query past data.

2. Step 2: Analyze options

   SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -2, CURRENT_TIMESTAMP)); uses DATEADD to subtract 2 hours from current time correctly; others use invalid or unsupported syntax.

3. Final Answer:

   SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -2, CURRENT_TIMESTAMP)); -> Option B

4. Quick Check:

   Use AT (TIMESTAMP => ...) with DATEADD for past data [OK]

Hint: Use AT (TIMESTAMP => DATEADD(...)) to query past data [OK]

Common Mistakes:

• Using unsupported keywords like BEFORE or FOR TIME TRAVEL
• Incorrect interval syntax
• Using OFFSET with negative seconds (not valid)

3. Given the table users had a row deleted 1 hour ago, what will this query return?
SELECT * FROM users AT (TIMESTAMP => DATEADD(hour, -1, CURRENT_TIMESTAMP));

medium

A. The table data including the deleted row as it was 1 hour ago.

B. An error because Time Travel cannot query deleted rows.

C. Only the deleted row from 1 hour ago.

D. The table data as it is now, without the deleted row.

Solution

1. Step 1: Understand Time Travel query effect

   Querying with AT (TIMESTAMP => ...) shows data as it was at that time, including deleted rows.

2. Step 2: Interpret the query

   The query asks for data 1 hour ago, so it returns all rows including the deleted one.

3. Final Answer:

   The table data including the deleted row as it was 1 hour ago. -> Option A

4. Quick Check:

   Time Travel shows past data including deleted rows [OK]

Hint: Time Travel shows full past data, not just current state [OK]

Common Mistakes:

• Assuming deleted rows are inaccessible
• Expecting only deleted rows returned
• Thinking it causes query errors

4. You tried to restore a dropped table using Time Travel but got an error. What is a likely cause?

medium

A. The Time Travel retention period has expired for that table.

B. You used the wrong SQL syntax for Time Travel.

C. The table was never created in the first place.

D. Time Travel does not support restoring dropped tables.

Solution

1. Step 1: Recall Time Travel retention limits

   Time Travel keeps data only for a set retention period (default 1 day).

2. Step 2: Analyze error cause

   If retention expired, data cannot be recovered, causing errors when restoring dropped tables.

3. Final Answer:

   The Time Travel retention period has expired for that table. -> Option A

4. Quick Check:

   Expired retention blocks recovery [OK]

Hint: Check retention period before restoring dropped tables [OK]

Common Mistakes:

• Assuming Time Travel keeps data forever
• Blaming syntax errors without checking retention
• Thinking dropped tables can't be restored at all

5. You accidentally updated many rows in a table 3 hours ago and want to recover the original data. Your Time Travel retention is 24 hours. Which approach correctly recovers the data?

hard

A. Run INSERT INTO table SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -3, CURRENT_TIMESTAMP)); to overwrite current data.

B. Run DELETE FROM table WHERE update_time < DATEADD(hour, -3, CURRENT_TIMESTAMP); to undo changes.

C. Use CREATE TABLE new_table AS SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -3, CURRENT_TIMESTAMP)); and replace the original table after verification.

D. Restore the entire database to the state 3 hours ago using Time Travel.

Solution

1. Step 1: Understand safe recovery method

   Directly overwriting current data risks data loss; safer to create a new table snapshot first.

2. Step 2: Verify and replace

   Creating a new table from past data lets you verify before replacing the original table.

3. Step 3: Analyze other options

   Run INSERT INTO table SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -3, CURRENT_TIMESTAMP)); to overwrite current data risks duplicate data; C does not revert updates; D is not supported at database level.

4. Final Answer:

   Use CREATE TABLE new_table AS SELECT * FROM table AT (TIMESTAMP => DATEADD(hour, -3, CURRENT_TIMESTAMP)); and replace the original table after verification. -> Option C

5. Quick Check:

   Recover by snapshot then replace [OK]

Hint: Recover past data into new table before replacing [OK]

Common Mistakes:

• Overwriting current data without backup
• Trying unsupported database-wide restore
• Using DELETE to undo updates