Struct Observed 

pub struct Observed {
    pub rows: u64,
    pub nulls: u64,
    pub distinct: bool,
    pub sorted: bool,
    pub min: Option<i128>,
    pub max: Option<i128>,
}

What the build saw while it read the parent key column.

This is the cardinality verification of section 2.3, and it is written into the header rather than recomputed because the build already had every value in front of it. Recording what was observed rather than what was declared is what keeps a wrong FOREIGN KEY from producing a wrong answer: a declaration that fails verification is reported, and no link is built.

Fields

rows: u64

Non-null values seen.

nulls: u64

Nulls seen, which are not keys and match no child row.

distinct: bool

Whether every non-null value was distinct. False means no link may be built at all.

sorted: bool

Whether the values arrived in non-decreasing order.

min: Option<i128>

The smallest non-null value, or None when there were none.

max: Option<i128>

The largest non-null value, or None when there were none.

Implementations

impl Observed

pub fn usable_as_parent(&self) -> bool

Whether this column can be the parent side of a link.

Distinctness is the whole requirement. A parent side that is not unique is not an error and is not a link: section 2.3 says it is a relationship that has to be executed as an ordinary join, and the planner is told so rather than left to find out.

Trait Implementations

impl Clone for Observed

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Observed

impl Debug for Observed

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Observed

impl PartialEq for Observed

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Observed