Dimension table and fact table in data warehouse

Catalog

1、 Dimension table

1.1 Dimension table

1.2 Characteristics of dimension table

2 Fact table

2.1 The concept of fact table

2.2 The characteristics of the fact table

2.3 Classification of fact tables

---

1、 Dimension table

1.1 Dimension table

Dimension tables are generally descriptive information about facts , Each dimension table corresponds to an object or a concept in the real world .

for example ： user , goods , date , Such area

1.2 Characteristics of dimension table

1） The dimension table has a wide range

2） Compared with the fact table , Fewer rows

3） The content is relatively fixed

For example, time dimension table ：

2 Fact table

2.1 The concept of fact table

In the fact table Each line represents a business event ( Place an order , payment , Refund, etc ).“ The facts ” This term represents a measure of business events （ Can count the number of times , Number , Amount, etc. ）

for example ,xxx One day I bought a product on a platform 250 element .

2.2 The characteristics of the fact table

1） Very big

2） The content is relatively narrow ： Fewer columns

3） Change often , A lot more will be added every day

2.3 Classification of fact tables

1） Transactional fact table

Take each event as a unit ,

for example , A sales order , A payment record, etc

2） Periodic snapshot fact table

Periodic snapshot fact table Not all data will be retained , Keep only data at fixed intervals

for example , Daily or monthly sales , Or monthly account balance

3） Cumulative snapshot fact table

The cumulative snapshot fact table is used to track changes in business facts

for example , The data warehouse may need to accumulate or store orders from the time of placing an order , To order items are packaged 、 transport 、 And the time point data of each business stage signed in to track the progress of the order declaration cycle .