Attaching and detaching partitions in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of attaching a partition

Given a partitioned table sales and a child table sales_2023 with matching structure, what is the output of the following command?

ALTER TABLE sales ATTACH PARTITION sales_2023 FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

What will be the result of this command?

PostgreSQL

ALTER TABLE sales ATTACH PARTITION sales_2023 FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

A Syntax error due to missing parentheses around the range values.

B Error because the range values overlap with an existing partition.

C Error because sales_2023 already contains data.

D The partition sales_2023 is attached successfully to sales.

💡 Hint

Check if the partition range matches the parent table's partitioning scheme.

The command attaches the child table sales_2023 as a partition for the specified range. If the range matches and no conflicts exist, it succeeds.

❓ query_result

intermediate

Result of detaching a partition

What happens when you run this command on a partitioned table orders with a partition orders_2022 attached?

ALTER TABLE orders DETACH PARTITION orders_2022;

PostgreSQL

ALTER TABLE orders DETACH PARTITION orders_2022;

A Error because the partition contains data.

B Syntax error due to missing CASCADE keyword.

C The partition orders_2022 is detached and becomes a standalone table.

D The partition is detached but all data is deleted.

💡 Hint

Detaching a partition removes it from the parent but keeps the data intact.

Detaching a partition removes the child table from the partitioned table but does not delete its data. It becomes a normal table.

📝 Syntax

advanced

Identify the syntax error in attaching a partition

Which option contains a syntax error when trying to attach a partition log_2023 to a partitioned table logs for the year 2023?

A ALTER TABLE logs ATTACH PARTITION log_2023 FOR VALUES IN ('2023');

B ALTER TABLE logs ATTACH PARTITION log_2023 FOR VALUES FROM '2023-01-01' TO '2024-01-01';

C ALTER TABLE logs ATTACH PARTITION log_2023 FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

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💡 Hint

Check the syntax for specifying range values in the ATTACH PARTITION command.

The FROM and TO values must be enclosed in parentheses. Option B misses the parentheses causing a syntax error.

🔧 Debug

advanced

Why does attaching a partition fail?

You try to attach a partition events_2023 to a partitioned table events using:

ALTER TABLE events ATTACH PARTITION events_2023 FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

The command fails with an error about overlapping ranges. What is the most likely cause?

A There is already a partition attached with a range that overlaps the specified range.

B The child table events_2023 has a different column structure than events.

C The parent table events is not partitioned.

D The child table events_2023 contains no data.

💡 Hint

Check existing partitions and their ranges for conflicts.

Partition ranges cannot overlap. If an existing partition covers any part of the specified range, attaching fails.

🧠 Conceptual

expert

Effect of detaching a partition on indexes

After detaching a partition archive_2020 from a partitioned table archive, what happens to the indexes defined on the partitioned table?

A The detached partition retains its own indexes independently of the parent table.

B All indexes on the detached partition are dropped automatically.

C The detached partition inherits all indexes from the parent table dynamically.

D The detached partition loses all indexes and must be reindexed manually.

💡 Hint

Consider how indexes are managed on partitions versus standalone tables.

Partitions have their own indexes. Detaching makes the partition a standalone table, so its indexes remain intact.

Practice

1. What does attaching a partition to a partitioned table in PostgreSQL do?

easy

A. It adds an existing table as a part of the partitioned table.

B. It deletes the data from the existing table.

C. It merges two tables into one without partitioning.

D. It creates a new partitioned table from scratch.

Solution

1. Step 1: Understand the purpose of attaching partitions

   Attaching a partition means linking an existing table to a partitioned table so it becomes one of its parts.

2. Step 2: Clarify what happens to data

   The data in the existing table remains intact and is now managed as part of the partitioned table.

3. Final Answer:

   It adds an existing table as a part of the partitioned table. -> Option A

4. Quick Check:

   Attaching partitions = adding existing table [OK]

Hint: Attaching means linking existing tables to partitions [OK]

Common Mistakes:

• Thinking attaching deletes data
• Confusing attaching with creating new tables
• Assuming attaching merges tables without partitioning

2. Which of the following is the correct syntax to attach a partition named part_2023 to a partitioned table sales in PostgreSQL?

easy

A. ALTER TABLE sales ADD PARTITION part_2023;

B. ALTER TABLE sales ATTACH PARTITION part_2023 FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

C. ALTER TABLE sales ATTACH part_2023 PARTITION;

D. ALTER TABLE sales ATTACH PARTITION part_2023;

Solution

1. Step 1: Recall the correct syntax for attaching partitions

   In PostgreSQL, when attaching an existing partitioned table, the syntax is ALTER TABLE sales ATTACH PARTITION part_2023; without specifying the value range, because the partition table already has the range defined.

2. Step 2: Check each option

   ALTER TABLE sales ATTACH PARTITION part_2023; uses the correct syntax. ALTER TABLE sales ATTACH PARTITION part_2023 FOR VALUES FROM ('2023-01-01') TO ('2024-01-01'); incorrectly includes the value range, which is only used when creating a new partition, not attaching an existing one. Options C and D use invalid syntax.

3. Final Answer:

   ALTER TABLE sales ATTACH PARTITION part_2023; -> Option D

4. Quick Check:

   Attach existing partition without value range [OK]

Hint: Attach existing partitions without value ranges using ATTACH PARTITION [OK]

Common Mistakes:

• Including FOR VALUES clause when attaching existing partitions
• Using ADD PARTITION instead of ATTACH PARTITION
• Incorrect keyword order

3. Given the following commands, what will be the result of querying SELECT count(*) FROM sales; after detaching the partition part_2022?

ALTER TABLE sales DETACH PARTITION part_2022;
SELECT count(*) FROM sales;

medium

A. The count includes rows from all partitions including part_2022.

B. The count will be zero because detaching deletes data.

C. The count excludes rows from part_2022 because it was detached.

D. The query will fail with an error because part_2022 is detached.

Solution

1. Step 1: Understand what detaching a partition does

   Detaching removes the partition from the partitioned table but does not delete its data; it becomes a standalone table.

2. Step 2: Effect on queries on the partitioned table

   After detaching, queries on the partitioned table no longer include data from the detached partition.

3. Final Answer:

   The count excludes rows from part_2022 because it was detached. -> Option C

4. Quick Check:

   Detached partitions excluded from parent queries [OK]

Hint: Detached partitions are excluded from parent table queries [OK]

Common Mistakes:

• Assuming detaching deletes data
• Thinking detached partitions still count in queries
• Expecting query errors after detach

4. You run the command ALTER TABLE sales DETACH PARTITION part_2023; but get an error saying the partition does not exist. What is the most likely cause?

medium

A. The partition part_2023 is not attached to the sales table.

B. You need to use DROP PARTITION instead of DETACH PARTITION.

C. The sales table is not partitioned.

D. You must detach partitions before attaching them.

Solution

1. Step 1: Check if the partition exists and is attached

   The error indicates part_2023 is not currently attached to sales, so it cannot be detached.

2. Step 2: Understand the difference between detach and drop

   DETACH PARTITION removes the link but keeps data; DROP PARTITION deletes data. Using drop won't fix a non-attached partition error.

3. Final Answer:

   The partition part_2023 is not attached to the sales table. -> Option A

4. Quick Check:

   Detach fails if partition not attached [OK]

Hint: Detach only works on attached partitions [OK]

Common Mistakes:

• Trying to detach partitions not attached
• Confusing DETACH with DROP
• Ignoring if table is partitioned

5. You have a large partitioned table orders partitioned by range on order_date. You want to archive data from 2020 by detaching the partition orders_2020 and then attaching it to a new partitioned table archived_orders. Which sequence of commands correctly achieves this without data loss?

hard

A. 1. ALTER TABLE archived_orders ATTACH PARTITION orders_2020;
2. ALTER TABLE orders DETACH PARTITION orders_2020;

B. 1. ALTER TABLE orders DETACH PARTITION orders_2020;
2. ALTER TABLE archived_orders ATTACH PARTITION orders_2020 FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');

C. 1. DROP TABLE orders_2020;
2. CREATE TABLE archived_orders PARTITION OF orders FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');

D. 1. ALTER TABLE orders ATTACH PARTITION orders_2020;
2. ALTER TABLE archived_orders DETACH PARTITION orders_2020;

Solution

1. Step 1: Detach the partition from the original table

   Use ALTER TABLE orders DETACH PARTITION orders_2020; to remove the partition without deleting data.

2. Step 2: Attach the detached partition to the new partitioned table

   Use ALTER TABLE archived_orders ATTACH PARTITION orders_2020 FOR VALUES FROM ('2020-01-01') TO ('2021-01-01'); to add it as a partition.

3. Final Answer:

   Detach from orders, then attach to archived_orders with value range. -> Option B

4. Quick Check:

   Detach then attach to new table preserves data [OK]

Hint: Detach first, then attach to new partitioned table [OK]

Common Mistakes:

• Dropping the partition instead of detaching
• Attaching before detaching
• Not specifying value ranges when attaching