Enum IdentCasing 

#[non_exhaustive]
pub enum IdentCasing {
    FoldUnquoted,
    FoldUnquotedUpper,
    FoldAll,
    FoldNone,
}

How a dialect folds identifiers for case-insensitive comparison.

SQL unquoted identifiers are case-insensitive, so grad(Temp*Temp, temp) must match — otherwise it silently differentiates to 0. The exact rule is per-dialect (F1):

• IdentCasing::FoldUnquoted — unquoted identifiers fold to lowercase; quoted identifiers keep their case. (DataFusion, Postgres, the generic dialect.)
• IdentCasing::FoldUnquotedUpper — the same rule with the opposite target case: unquoted identifiers fold to uppercase. (Snowflake, Oracle.)
• IdentCasing::FoldAll — all identifiers fold, quoted included, so case never distinguishes two columns. (DuckDB, Spark, MySQL.)
• IdentCasing::FoldNone — no identifier folds; x and X are simply different columns. (ClickHouse.)

The two unquoted-only policies are not interchangeable, and the difference is visible rather than cosmetic: X matches "X" under FoldUnquotedUpper and "x" under FoldUnquoted. Applying the wrong one to Snowflake does not just miss — it can match the other column and return a confidently wrong nonzero derivative.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

FoldUnquoted

Fold unquoted identifiers to lowercase (DataFusion / Postgres / generic).

FoldUnquotedUpper

Fold unquoted identifiers to uppercase (Snowflake / Oracle).

FoldAll

Fold every identifier, quoted included (DuckDB / Spark / MySQL).

FoldNone

Fold nothing; identifiers are compared as written (ClickHouse).

Implementations

impl IdentCasing

pub fn fold(self, id: &Ident) -> String

The comparison key for a single identifier under this policy.

Only equality of the returned keys is meaningful — which case they fold to is arbitrary, so long as an unquoted identifier and a quoted one land on the same key exactly when the engine would resolve them to the same column.

Trait Implementations

impl Clone for IdentCasing

fn clone(&self) -> IdentCasing

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for IdentCasing

impl Debug for IdentCasing

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

Formats the value using the given formatter.

impl Eq for IdentCasing

impl PartialEq for IdentCasing

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for IdentCasing