The Role of Primary Keys and Partition Keys in ClickHouse (Design Best Practices)

What is a Primary Key?

Definition of a Primary Key

In ClickHouse, the primary key (Primary Key) is a unique and non-repeating column or combination of columns used to identify unique values for each record.

Usage Scenarios of a Primary Key

1. Data Integrity: Ensure data is not added redundantly.

2. Fast Lookup: Quickly locate specific records.

What is a Partition Key?

Definition of a Partition Key

In ClickHouse, the partition key (Partition Key) is a column or combination of columns used to organize large tables; they are used for partitioning tables to improve data storage and retrieval efficiency.

Usage Scenarios of a Partition Key

1. Data Storage Efficiency: Reduce table size.

2. Fast Retrieval: Quickly find the required data.

Design Principles for Primary Keys and Partition Keys

1. Single Column Primary Key: When using a single column primary key, the table width should be less than or equal to 1000.

2. Composite Primary Key: When using a composite primary key, the table width should be less than or equal to 500.

3. Design Principles for Partition Keys

• Use unique values.
• Select columns consistent with the primary key.
• Do not reuse both the primary key and partition key simultaneously.
• Maintain a reasonable table width.