Partition types (range, list, hash) in PostgreSQL - Step-by-Step Execution

Concept Flow - Partition types (range, list, hash)

Start: Create Partitioned Table

↓

Choose Partition Type

↓

Range

↓

Define Ranges

↓

Create Partitions

↓

Insert Data Routed to Correct Partition

↓

Query Data Efficiently

You start by creating a partitioned table, then pick one partition type: range, list, or hash. Each type defines how data is split into partitions. Data inserts go to the right partition, making queries faster.

Execution Sample

PostgreSQL

CREATE TABLE sales (
  id INT,
  sale_date DATE,
  region TEXT
) PARTITION BY RANGE (sale_date);

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

This creates a sales table partitioned by date ranges, then creates a partition for all sales in 2023.

Execution Table

Step	Action	Partition Type	Partition Definition	Data Routing Example	Result
1	Create main table with partitioning	Range	PARTITION BY RANGE (sale_date)	N/A	Table 'sales' created as partitioned
2	Create partition for 2023	Range	FOR VALUES FROM ('2023-01-01') TO ('2024-01-01')	N/A	Partition 'sales_2023' created
3	Insert row with sale_date = '2023-06-15'	Range	N/A	Falls into 2023 partition	Row stored in 'sales_2023'
4	Create main table with list partitioning	List	PARTITION BY LIST (region)	N/A	Table 'customers' created as partitioned
5	Create partition for region 'North'	List	FOR VALUES IN ('North')	N/A	Partition 'customers_north' created
6	Insert row with region = 'North'	List	N/A	Falls into 'North' partition	Row stored in 'customers_north'
7	Create main table with hash partitioning	Hash	PARTITION BY HASH (id) PARTITIONS 4	N/A	Table 'orders' created as partitioned
8	Create 4 hash partitions	Hash	FOR VALUES WITH (MODULUS 4, REMAINDER 0) FOR VALUES WITH (MODULUS 4, REMAINDER 1) FOR VALUES WITH (MODULUS 4, REMAINDER 2) FOR VALUES WITH (MODULUS 4, REMAINDER 3)	N/A	Partitions 'orders_0' to 'orders_3' created
9	Insert row with id = 7	Hash	N/A	Hash(id) mod 4 = 3	Row stored in 'orders_3'
10	Query data	All	N/A	Query optimizer targets relevant partitions	Faster query execution
11	End	N/A	N/A	N/A	Partitioning setup complete

💡 All partitions created and data routed correctly; queries can now use partitions for efficiency.

Variable Tracker

Variable	Start	After Step 2	After Step 5	After Step 8	Final
Partitioned Table	None	sales (Range)	sales, customers (Range, List)	sales, customers, orders (Range, List, Hash)	All 3 tables partitioned
Partitions Created	0	1 (sales_2023)	2 (sales_2023, customers_north)	6 (sales_2023, customers_north, orders_0..orders_3)	6 partitions total
Data Insert Example	N/A	Row with sale_date=2023-06-15 in sales_2023	Row with region='North' in customers_north	Row with id=7 in orders_3	Rows routed to correct partitions

Key Moments - 3 Insights

Why do we need to define ranges or lists when creating partitions?

Because PostgreSQL needs clear rules to decide which partition each row belongs to. See execution_table rows 2 and 5 where partitions are defined with ranges or lists.

How does hash partitioning decide where to put data?

It uses a hash function on the partition key and divides by the number of partitions. For example, in row 9, id=7 goes to partition 3 because hash(7) mod 4 = 3.

Can data be stored outside partitions in a partitioned table?

No, all data must fit into one of the defined partitions. If no partition matches, insert fails. This is why defining partitions correctly is important.

Visual Quiz - 3 Questions

Look at the execution_table row 3. Where is a row with sale_date = '2023-06-15' stored?

A In the partition 'sales_2023'

B In the main table 'sales'

C In a hash partition

D It is rejected because no partition matches

💡 Hint

Check the 'Data Routing Example' and 'Result' columns in row 3 of execution_table.

According to variable_tracker, how many partitions exist after step 8?

A 3

B 6

C 4

D 8

💡 Hint

Look at the 'Partitions Created' row after step 8 in variable_tracker.

If you insert a row with id=10 into the hash partitioned table with 4 partitions, which partition will it go to?

A orders_4

B orders_3

C orders_2

D orders_1

💡 Hint

Recall hash partitioning uses hash(id) mod number_of_partitions; see example in execution_table row 9.

Concept Snapshot

Partition types in PostgreSQL:
- RANGE: splits data by ranges of values (e.g., dates)
- LIST: splits data by specific values (e.g., regions)
- HASH: splits data by hashing a key (e.g., id)
Define partitions with FOR VALUES clause.
Data inserts go to matching partition.
Queries can target partitions for speed.

Full Transcript

Partitioning in PostgreSQL means splitting a big table into smaller pieces called partitions. You first create a main table and choose a partition type: range, list, or hash. Range partitions split data by value ranges, like dates. List partitions split by specific values, like regions. Hash partitions split by a hash function on a key, like an id. You create partitions with rules that tell PostgreSQL where to put data. When you insert data, PostgreSQL routes it to the right partition. This helps queries run faster because they only look at relevant partitions. The execution table shows steps creating tables and partitions, inserting data, and how data is routed. The variable tracker shows how many partitions exist and where data goes. Key moments explain why defining partitions is important and how hash partitioning works. The quiz tests understanding of data routing and partition counts. The snapshot summarizes the types and usage of partitions.

Practice

1. Which partition type in PostgreSQL is best suited for dividing a table based on continuous ranges of values, such as dates or numbers?

easy

A. HASH partitioning

B. LIST partitioning

C. RANGE partitioning

D. NONE partitioning

Solution

1. Step 1: Understand partition types

   RANGE partitions split data into continuous ranges, like dates or numeric intervals.

2. Step 2: Match partition type to use case

   Since the question asks about continuous ranges, RANGE partitioning fits best.

3. Final Answer:

   RANGE partitioning -> Option C

4. Quick Check:

   Continuous ranges = RANGE partitioning [OK]

Hint: Continuous values? Choose RANGE partitioning [OK]

Common Mistakes:

• Confusing LIST with RANGE for continuous data
• Thinking HASH is for ordered ranges
• Assuming NONE is a valid partition type

2. Which of the following is the correct syntax to create a LIST partitioned table in PostgreSQL?

easy

A. CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region);

B. CREATE TABLE sales PARTITION BY LIST region (id INT, region TEXT);

C. CREATE TABLE sales (id INT, region TEXT) PARTITION BY RANGE (region);

D. CREATE TABLE sales (id INT, region TEXT) PARTITION BY HASH (region);

Solution

1. Step 1: Identify correct PARTITION BY syntax

   PostgreSQL syntax requires PARTITION BY followed by partition type and column in parentheses after table columns.

2. Step 2: Check each option

   CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region); uses correct syntax: columns first, then PARTITION BY LIST (region). Options A, B, C have syntax errors or wrong partition type.

3. Final Answer:

   CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region); -> Option A

4. Quick Check:

   Correct syntax = CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region); [OK]

Hint: PARTITION BY type (column) after columns [OK]

Common Mistakes:

• Placing PARTITION BY before column definitions
• Using wrong partition type for LIST
• Missing parentheses around partition column

3. Given the following partitioned table and inserts:

CREATE TABLE orders (
  order_id INT,
  order_date DATE
) PARTITION BY RANGE (order_date);

CREATE TABLE orders_2023 PARTITION OF orders
  FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

INSERT INTO orders VALUES (1, '2023-06-15');
INSERT INTO orders VALUES (2, '2022-12-31');

What will happen when the second insert is executed?

medium

A. The row is inserted into orders_2023 partition

B. The row is rejected with a constraint violation error

C. The row is inserted into a default partition automatically

D. The row is inserted into the parent table without partition

Solution

1. Step 1: Understand RANGE partition boundaries

   The orders_2023 partition accepts dates from 2023-01-01 up to but not including 2024-01-01.

2. Step 2: Check the inserted date '2022-12-31'

   This date is before the partition range, so no matching partition exists for it.

3. Step 3: Behavior on no matching partition

   PostgreSQL rejects inserts that don't fit any partition unless a default partition exists (none here).

4. Final Answer:

   The row is rejected with a constraint violation error -> Option B

5. Quick Check:

   Out-of-range insert = error [OK]

Hint: Out-of-range insert without default partition causes error [OK]

Common Mistakes:

• Assuming automatic default partition insertion
• Thinking parent table stores unmatched rows
• Ignoring partition range boundaries

4. Consider this partitioned table creation:

CREATE TABLE employees (
  emp_id INT,
  department TEXT
) PARTITION BY LIST (department);

CREATE TABLE employees_sales PARTITION OF employees FOR VALUES IN ('Sales');
CREATE TABLE employees_hr PARTITION OF employees FOR VALUES IN ('HR');

Which error will occur if you try to insert INSERT INTO employees VALUES (1, 'Marketing');?

medium

A. No partition found for value 'Marketing', insert fails

B. Syntax error due to missing partition

C. Row inserted into employees_sales partition by default

D. Row inserted into parent table without partition

Solution

1. Step 1: Check defined partitions

   Partitions exist only for 'Sales' and 'HR' departments.

2. Step 2: Check inserted value 'Marketing'

   'Marketing' is not listed in any partition's VALUES list.

3. Step 3: PostgreSQL behavior on unmatched LIST value

   Without a default partition, insert fails with no matching partition error.

4. Final Answer:

   No partition found for value 'Marketing', insert fails -> Option A

5. Quick Check:

   Unlisted LIST value = insert failure [OK]

Hint: LIST partition needs matching value or default partition [OK]

Common Mistakes:

• Assuming insert goes to any partition by default
• Expecting parent table to store unmatched rows
• Confusing syntax error with runtime insert error

5. You want to evenly distribute a large table's rows across 4 partitions to improve query performance without caring about specific value ranges. Which partition type and setup is best in PostgreSQL?

hard

A. Use no partitioning and rely on indexes.

B. Use LIST partitioning with 4 specific values.

C. Use RANGE partitioning on a numeric column with 4 ranges.

D. Use HASH partitioning with 4 partitions.

Solution

1. Step 1: Understand partitioning goals

   The goal is even distribution across 4 partitions without caring about value ranges.

2. Step 2: Match partition type to goal

   HASH partitioning evenly distributes rows based on a hash function, ideal for this case.

3. Step 3: Evaluate other options

   RANGE and LIST require specific ranges or values, not suitable for even spread without criteria. No partitioning misses distribution benefits.

4. Final Answer:

   Use HASH partitioning with 4 partitions. -> Option D

5. Quick Check:

   Even distribution = HASH partitioning [OK]

Hint: Even spread without ranges? Choose HASH partitioning [OK]

Common Mistakes:

• Using RANGE or LIST when no value grouping needed
• Thinking indexes replace partitioning benefits
• Confusing HASH with LIST partitioning