What does the high cardinality data feature mean

In SQL, cardinality is defined as the number of unique data ina data column.

High-cardinality is defined as the fact that data ina data column is essentially non-repeated, or that the rate of duplication is very low.

For example, common identification numbers, email addresses, user names and so on can be considered as high cardinality data. For example, we often define the USER_ID field in the USERS table, and the data in this field is usually defined as 1 through N.

Each time a new user is inserted into the USERS table as a record, a new record will be created and the field USER_ID will use a new data to identify the inserted data.

Because the data inserted into USER_ID is unique, the data technique for this field can be considered high-cardinality data.

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