Data warehouse interview question preparation

One 、 How to understand data system

Including the data model 、 Data tiering 、 Data subject division 、 Data governance 、 Metadata management 、 Data security permissions 、 A complete data warehouse service system for data warehouse visual products

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Two 、 What is the goal of shucang

Data quality and data service

Data quality ： Orderly 、 Organize and store data in a structured way , Avoid duplicate construction and data inconsistency , To ensure the normalization of data

Data services ： Improve the data experience , Including the accuracy of data 、 Data products enhance the body feeling of data visualization services

Questioning ： How to understand classification, organization and storage

Classified Organization ： Organize the topic division mapped to the data warehouse （ The transverse )、 layered （ The longitudinal )

Storage ： For lifecycle management 、 Data governance

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3、 ... and 、 The fact table is divided into several kinds

1. Based on layering 、 And schedule type

• According to layering , Detailed fact table of atomic index composition DWD, Derived indicators form a summary fact table DWS

• The detailed fact table is divided into ： Fact sheet of affairs 、 Cumulative snapshot fact table 、 Periodic snapshot fact table

2. Expand to say ...

• Transactional fact tables are used to describe business processes , Track the measurement time of a certain point in space or time , It holds the most atomic data , It can also be called “ Atomic fact table ”

• Periodic snapshot fact table with regular 、 Record facts at predictable intervals , Time intervals such as every day 、 monthly 、 Annual wait .

• The cumulative snapshot fact table is used to express the key step time between the beginning and end of the process , Covering the entire life cycle of the process , It usually has multiple date fields to record key time points , When the process changes with the life cycle , Records are also modified as the process changes .

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Four 、 What are the contents of the indicators

1. Content ： Atomic index 、 Derived indicators 、 Derivatives

2. Relationship

• Derived indicators = Atomic index + cycle time + Modifiers

• Derived indicators are divided into ： Transactional indicators 、 Stock index and compound index

  • Transactional indicators ： It refers to the indicators for measuring business activities . for example ： Number of new products issued , Order payment amount . It's a modifier + Atomic index

  • Stock index ： Refers to the entity object ( Such as commodities 、 members ) Statistics of some states . for example ： The total number of goods is a modifier + Atomic index + cycle ( Generally, the history ends at a certain time )

  • Composite index ： It is compounded on the basis of transaction indicators and stock indicators .

3. Association in business

• Atomic index 、 Modifier types and modifiers , Directly under the business process , The modifier inherits the data field of the modifier type , for example ：A Channel payment amount , Through payment, you can know that it belongs to the payment primary domain , The channel is used to decorate the subject field of the channel , It can be a cross domain combination
• Multiple modifiers can be selected for derived indicators , The relationship between modifiers is “ or ” perhaps “ And ”, for example ： New customers pay for electronic products , Modifiers ： New customers and electronic products
• The derived index only belongs to an atomic index , Inherit the data field of the atomic indicator , Independent of the data field of the modifier . for example ：A Channel payment amount , Or is it the amount of payment
• generally speaking , If two behaviors occur at the same time , More than one modifier is required 、 Generate a derived indicator , Then select the behavior later in time to create an atomic indicator , Choose the behavior that comes first in time to create a modifier , for example ：A Channel payment amount , A transaction that first goes through a channel and then results , The channel is before the comparison , After that, the payment amount will be generated , Atomic indicators are relatively backward

4. Extend the entire architecture

• Determine the data warehouse of enterprise level and business department , Then confirm the subject field , And then sort out the business process , Basic data are atomic indicators , Fall on DWD Form a detailed fact sheet , Add modifiers to become derived indicators , Form mild DWS Summary fact sheet , The dimension will be associated with the fact table through dimension degradation .

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5、 ... and 、 The dimension degenerates to the difference between a single transactional fact table and a wide table

The former still represents the fact table of decoupled business process , A wide table is a table that integrates across business processes , Emphasize multiple business processes