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. In this introduction to Declarative SQL, Joe Celko demonstrates how you can write portable code that performs well and executes some complex logic, merely by creating unique constraints.


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Set-based Constraint Violation Reporting in SQL Server

  • Article

When you're importing data into an RDBMS in bulk and an exception condition is raised because of a constraint violation, you generally need to fix the problem with the data and try again. The error won't tell you which rows are causing the violation. What if you've thousands of rows to search when it happens? There are solutions, writes William Sisson.


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SQL Server Unique Constraints for Large Text Columns

  • Article

We are storing large text and URLs that are over 900 bytes in some of our tables and have a requirement to enforce uniqueness in those columns. But SQL Server has a limitation that index size can't be over 900 bytes. How do I enforce uniqueness in these columns and is it possible to achieve this in SQL Server 2005 and above? What are my different options to solve this problem? I heard that we can use CHECKSUM to create a hash, but is it possible to avoid collisions in the hash value as we are storing millions of rows?


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