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Which is why it's worth even specifying 1NF. That doesn't mean that the relational algebra does not allow for them. I think the reason people even ask question

Which is why it's worth even specifying 1NF. That doesn't mean that the relational algebra does not allow for them. I think the reason people even ask questions like what does 1NF even mean is because they're not learning relational algebra, they are learning SQL. So if every table is in 1NF by default, it begs the question what is the point of 1NF? And the point is that the relational algebra is bigger than SQL, a realization that leads you to potentially interesting projects like CJ Date's efforts to build truly relational databases.

goto11 5y ago
But isn't Codd's relational algebra based on 1NF relations? The point of 1NF is (among other things) to make the algebra simpler because you don't need to handle nested relations. A database built on non-1NF relations would be very different from Codd's vision.
CRConrad 5y ago
> So if every table is in 1NF by default, it begs the question what is the point of 1NF? Your premise isn't fulfilled: Not every SQL table is in 1NF by default, it's quite easy to fuck that up. As illustrated by the whole "list of telephone numbers in a single column" point discussed here.
- goto11 5y ago
  This is what the article discuss. 1NF is about eliminating nested tables, which is not supported by SQL. Dumping a list of phone numbers into a string does not violate 1NF because a string is still just a single value from the perspective of the database.
  - CRConrad 5y ago
    The article is wrong: There is no "from the perspective of the database" here. Normalisation is a logical-level process, not physical. What we're using the database to do is to store information about the real world. 1NF is about eliminating nested relations. A list of telephone numbers is a relation -- a one-row table, if you will. > Normalized relations, and the relationship between one normalized relation and another, mirror real-world concepts and their interrelationships. -- https://en.wikipedia.org/wiki/Database_normalization#Minimize_redesign_when_extending_the_database_structure https://en.wikipedia.org/wiki/Database_normalization#Minimiz... In the real world, a phone call is to a single phone number, not to a list of them. > To satisfy First normal form, each column of a table must have a single value. Columns which contain sets of values or nested records are not allowed. -- https://en.wikipedia.org/wiki/Database_normalization#Satisfying_1NF https://en.wikipedia.org/wiki/Database_normalization#Satisfy... A list of telephone numbers is a set of values, not a single value. Several strings "in one".
    - goto11 5y ago
      > 1NF is about eliminating nested relations. Absolutely agree, this is the definition of 1NF. So if you have a relation which has an attribute which has a domain which itself include relations - then you have a 1NF violation. "From the perspective of the database" is perhaps too vague (although Codd uses almost the same phrasing), the question is if the value is atomic with regard to the relational operators (project, join etc.). Can you INSERT a tuple into a value? Then the value is a relation. I get that at a certain abstraction level a comma separated string value could be considered a list or a relation. But then it would be at a different abstraction level than the one where the containing table is a relation. Because you can select rows and column from this outer relation using the relational operators, but you cant do the same for a relation encoded into a string value.

goto11 5y ago

But isn't Codd's relational algebra based on 1NF relations? The point of 1NF is (among other things) to make the algebra simpler because you don't need to handle nested relations. A database built on non-1NF relations would be very different from Codd's vision.

CRConrad 5y ago

> So if every table is in 1NF by default, it begs the question what is the point of 1NF? Your premise isn't fulfilled: Not every SQL table is in 1NF by default, it's quite easy to fuck that up. As illustrated by the whole "list of telephone numbers in a single column" point discussed here.

goto11 5y ago
This is what the article discuss. 1NF is about eliminating nested tables, which is not supported by SQL. Dumping a list of phone numbers into a string does not violate 1NF because a string is still just a single value from the perspective of the database.
- CRConrad 5y ago
  The article is wrong: There is no "from the perspective of the database" here. Normalisation is a logical-level process, not physical. What we're using the database to do is to store information about the real world. 1NF is about eliminating nested relations. A list of telephone numbers is a relation -- a one-row table, if you will. > Normalized relations, and the relationship between one normalized relation and another, mirror real-world concepts and their interrelationships. -- https://en.wikipedia.org/wiki/Database_normalization#Minimize_redesign_when_extending_the_database_structure https://en.wikipedia.org/wiki/Database_normalization#Minimiz... In the real world, a phone call is to a single phone number, not to a list of them. > To satisfy First normal form, each column of a table must have a single value. Columns which contain sets of values or nested records are not allowed. -- https://en.wikipedia.org/wiki/Database_normalization#Satisfying_1NF https://en.wikipedia.org/wiki/Database_normalization#Satisfy... A list of telephone numbers is a set of values, not a single value. Several strings "in one".
  - goto11 5y ago
    > 1NF is about eliminating nested relations. Absolutely agree, this is the definition of 1NF. So if you have a relation which has an attribute which has a domain which itself include relations - then you have a 1NF violation. "From the perspective of the database" is perhaps too vague (although Codd uses almost the same phrasing), the question is if the value is atomic with regard to the relational operators (project, join etc.). Can you INSERT a tuple into a value? Then the value is a relation. I get that at a certain abstraction level a comma separated string value could be considered a list or a relation. But then it would be at a different abstraction level than the one where the containing table is a relation. Because you can select rows and column from this outer relation using the relational operators, but you cant do the same for a relation encoded into a string value.