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DDL UNIQUE constraints ensure that the data contained in a column, or a group of columns, is unique among all the rows in the table. The data contained in the column or columns involved is, therefore, useful to uniquely identify a row in the relevant table.

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Unique constraint for single structure that simulates relations between tables

Imagine I have several tables in SQL Server 2016: Cat Cat carrier Cat transit box Cat car Every object can be stored in higher level, but not necessarily directly one above with N-to-1. So a cat can …