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I want to write a constraint using relational algebra that the current date has to be less than the expiry date in a specific relation. I'm aware this is easy in SQL, but not sure how to do it in relational algebra.

philipxy
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RaoulDuke
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  • A constraint is a true statement or part of one. A relational algebra query returns a relation. What do you mean, "write a constraint using relational algebra"? PS There are many RAs (relational algebras). They differ in operators & even what a relation is. Give operator definitions & your reference for yours. Eg textbook name, edition & page. What DBMS/system are you using, what context are you doing this in? How are functions accessible to queries? [mre] PS [What is the equivalent, in Relational Algebra, of a SQL Table Relationship?](https://stackoverflow.com/q/48905581/3404097) – philipxy Mar 11 '22 at 20:32
  • Possible duplicate of [expressing constraints in relational algebra](https://stackoverflow.com/q/28457182/3404097) – philipxy Mar 12 '22 at 03:39

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Use TODAY, which would read naturally in a diagram/algebra.

Bohemian
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