What is the difference between fact table and dimension table?

What is the difference between fact table and dimension table?

The fact table contains business facts (or measures), and foreign keys which refer to candidate keys (normally primary keys) in the dimension tables. Contrary to fact tables, dimension tables contain descriptive attributes (or fields) that are typically textual fields (or discrete numbers that behave like text).

Which data can be stored in dimension table?

Dimension tables group the data in the database when the business creates reports. For example, you can group sales targets by country, product, or retailer, and those groupings are stored in dimension tables. Each dimension table contains a number of columns and attributes that are used to describe business processes.

What should be in a fact table?

In data warehousing, a fact table consists of the measurements, metrics or facts of a business process. It is located at the center of a star schema or a snowflake schema surrounded by dimension tables. The grain of a sales fact table might be stated as “sales volume by day by product by store”.

What is the grain of a fact table?

The grain of a fact table defines the lowest level of detail that the fact table is divided into. For more information about grain in fact tables, see Fact Table.

What are the three types of fact tables?

Ralph Kimball’s dimensional data modeling defines three types of fact tables….These are:

• Transaction fact tables.
• Periodic snapshot tables, and.
• Accumulating snapshot tables.

What is fact table example?

An example of a fact table. In the schema below, we have a fact table FACT_SALES that has a grain that gives us the number of units sold by date, by store, and product. All other tables such as DIM_DATE , DIM_STORE and DIM_PRODUCT are dimensions tables. This schema is known as the star schema.

Can fact table have primary key?

The fact table also has a primary (composite) key that is a combination of these four foreign keys. As a rule, each foreign key of the fact table must have its counterpart in a dimension table. Therefore a dimension table can also be a fact table for a separate star schema.

Can you change the grain of a fact table?

You can do this in a few steps: like this if memory serves: Your market data should be presented to the cube as a view. If it is not create one and in the DSV replace the table with “another table” and point it to the new view.

What are the three types of facts?

There are three types of facts:

• Additive: Additive facts are facts that can be summed up through all of the dimensions in the fact table.
• Semi-Additive: Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others.

What is the purpose of fact table?

A fact table stores quantitative information for analysis and is often denormalized. A fact table works with dimension tables. A fact table holds the data to be analyzed, and a dimension table stores data about the ways in which the data in the fact table can be analyzed.

How is the grain of a fact table?

The grain of this type of fact table is one row per process; it has many roles of the date dimension; and the fact table rows are updated multiple times over the life of the process (hence the name accumulating snapshot). You can read more about accumulating snapshot fact tables in The Data Warehouse Toolkit, pages 128-134.

Is the grain of a table a unique query?

The problem with assuming the grain by unique query is that there may be multiple queries that seem to indicate unique combinations of your data, but only one of them was probably intended as the grain. You must be logged in to reply to this topic.

Why do you need more fields in a fact table?

The more fields you have as a grain in your fact table means the more dimension you are connected to, and it means more power for slicing and dicing. On the other hand, more fields, also mean row numbers will increase too, and you will need more memory to store the data.

Where do we store measurements in fact tables?

Fact tables are where we store these measurements. They hold business data that can be aggregated across dimension combinations. But the fact is that fact tables are not so easily described – they have flavors of their own. In this article, we’ll answer some basic questions about fact tables, and examine the pros and cons of each type.