<P> Examples of tables (or views) that would not meet this definition of first normal form are: </P> <Ul> <Li> A table that lacks a unique key constraint . Such a table would be able to accommodate duplicate rows, in violation of condition 3 . </Li> <Li> A view whose definition mandates that results be returned in a particular order, so that the row - ordering is an intrinsic and meaningful aspect of the view . This violates condition 1 . The tuples in true relations are not ordered with respect to each other . </Li> <Li> A table with at least one nullable attribute . A nullable attribute would be in violation of condition 4, which requires every column to contain exactly one value from its column's domain . It should be noted, however, that this aspect of condition 4 is controversial . It marks an important departure from Codd's later vision of the relational model, which made explicit provision for nulls . </Li> </Ul> <Li> A table that lacks a unique key constraint . Such a table would be able to accommodate duplicate rows, in violation of condition 3 . </Li> <Li> A view whose definition mandates that results be returned in a particular order, so that the row - ordering is an intrinsic and meaningful aspect of the view . This violates condition 1 . The tuples in true relations are not ordered with respect to each other . </Li>

When is a table said to be in 1nf