List partitioning by category in PostgreSQL - Step-by-Step Execution

Concept Flow - List partitioning by category

Create main partitioned table

↓

Define partition key column

↓

Create partitions for each category

↓

Insert data into main table

↓

PostgreSQL routes data to correct partition

↓

Query data from main table

↓

Data fetched from relevant partitions

The flow shows creating a main table partitioned by category, defining partitions, inserting data, and querying which accesses the correct partitions.

Execution Sample

PostgreSQL

CREATE TABLE products (
  id SERIAL PRIMARY KEY,
  name TEXT,
  category TEXT
) PARTITION BY LIST (category);

CREATE TABLE products_electronics PARTITION OF products FOR VALUES IN ('electronics');

INSERT INTO products VALUES (1, 'Phone', 'electronics');

This code creates a partitioned table by category, adds a partition for 'electronics', and inserts a product routed to that partition.

Execution Table

Step	Action	Table Affected	Partition Key Value	Result/State
1	Create main table with LIST partition on category	products	N/A	Main table created, ready for partitions
2	Create partition for category 'electronics'	products_electronics	'electronics'	Partition created for 'electronics' category
3	Insert product with category 'electronics'	products	'electronics'	Row routed to products_electronics partition
4	Query products where category = 'electronics'	products	'electronics'	Data fetched from products_electronics partition
5	Insert product with category 'furniture'	products	'furniture'	Error: no partition for 'furniture' category
6	Create partition for category 'furniture'	products_furniture	'furniture'	Partition created for 'furniture' category
7	Insert product with category 'furniture'	products	'furniture'	Row routed to products_furniture partition
8	Query all products	products	All	Data fetched from all partitions
9	End of operations	N/A	N/A	Execution complete

💡 Execution stops after all partitions created and data inserted; errors occur if inserting without matching partition.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	Final
products table	Empty	Contains 1 row in electronics partition	No change (error on insert)	Contains 1 row in electronics partition and 1 row in furniture partition	Contains rows in electronics and furniture partitions
products_electronics partition	Empty	1 row (Phone)	1 row (Phone)	1 row (Phone)	1 row (Phone)
products_furniture partition	Not created	Not created	Not created	1 row (Furniture item)	1 row (Furniture item)

Key Moments - 3 Insights

Why does inserting a row with a category that has no partition cause an error?

Because PostgreSQL requires a matching partition for the partition key value; see execution_table row 5 where insert fails without a partition.

How does PostgreSQL decide which partition to put a new row into?

It uses the partition key column value to route the row to the matching partition, as shown in execution_table rows 3 and 7.

When querying the main table, how does PostgreSQL fetch data?

It queries only the relevant partitions based on the query filter or all partitions if no filter, as in execution_table rows 4 and 8.

Visual Quiz - 3 Questions

Look at the execution_table at step 5, what happens when inserting a product with category 'furniture' before its partition exists?

A The row is inserted into the main table without partition

B An error occurs because no matching partition exists

C The row is inserted into the 'electronics' partition

D PostgreSQL creates a new partition automatically

💡 Hint

Check execution_table row 5 showing the insert error due to missing partition

According to variable_tracker, after step 7, which partitions contain rows?

A Both products_electronics and products_furniture

B Only products_furniture

C Only products_electronics

D No partitions contain rows

💡 Hint

See variable_tracker rows for products_electronics and products_furniture after step 7

In the concept_flow, what happens immediately after inserting data into the main table?

A Partitions are created automatically

B Data is stored only in the main table

C PostgreSQL routes data to the correct partition

D Data is duplicated in all partitions

💡 Hint

Look at the flow step after 'Insert data into main table' showing routing to partitions

Concept Snapshot

List Partitioning by Category in PostgreSQL:
- Create main table with PARTITION BY LIST (column)
- Create partitions for each category value
- Insert rows into main table
- Rows routed to matching partition
- Queries access relevant partitions
- Insert fails if no matching partition exists

Full Transcript

List partitioning by category in PostgreSQL involves creating a main table partitioned by a list of values in a column, such as category. You then create partitions for each category value you want to store separately. When you insert data into the main table, PostgreSQL automatically routes the row to the correct partition based on the category value. If you try to insert a row with a category that has no partition, an error occurs. Queries on the main table fetch data from the relevant partitions, improving performance and organization.