May 2018
Intermediate to advanced
576 pages
30h 25m
English
Uniqueness is always enforced by an index.
Each index is defined with a data type operator. When a new row is inserted or the set of column values is updated, we use the operator to search for existing values that conflict with the new data.
So, to enforce uniqueness, we need an index and a search operator defined on the data types of the columns. When we define normal UNIQUE constraints, we simply assume that we mean the equality operator (=) for the data type. The EXCLUDE syntax offers a richer syntax to allow us to express the same problem with different data types and operators.