Unique constraint

External Article

Declarative SQL: Using UNIQUE Constraints

  • Article

In SQL, you can express the logic of what you want to accomplish without spelling out the details of how the database should do it. Nowhere is this more powerful than in constraints. SQL is declarative, and Joe Celko demonstrates, in his introduction to Declarative SQL, how you can write portable code that performs well and executes some complex logic, merely by creating unique constraints.

2015-12-29

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Question of the Day

Using table variables in T-SQL

What happens if you run the following code in SQL Server 2022+? 

declare @t1 table (id int);

insert into @t1 (id) values (NULL), (1), (2), (3);

select count(*)
from @t1
where @t1.id is distinct from NULL;
 

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