Enum Casing 

pub enum Casing {
    Upper,
    Lower,
    Preserve,
}

How unquoted identifiers fold for identity in consumers such as planners.

The parser still interns the exact source text; this value describes later identity behaviour without losing render fidelity.

One tri-state models a single identity fold shared by every unquoted identifier — table, column, and alias alike. That single-fold model is a deliberate, parity-matching choice, not a gap: datafusion-sqlparser-rs, the drop-in target, does not key case sensitivity by identifier kind either, so one knob already meets parity and per-kind folding would be strictly more expressive than parity requires. It also keeps the dialect model minimal. Self::Lower approximates the MySQL/T-SQL column rule — “case-preserving storage, case-insensitive comparison” — closely: fold lower for identity while the interned text still renders exactly as written (folding is layered onto the exact form, never baked into the parse).

Known limitation: per-identifier-kind sensitivity

MySQL and T-SQL are case-insensitive for columns/aliases, but table and database name sensitivity is a deployment setting (MySQL lower_case_table_names, the T-SQL server/database collation). A case-insensitive column beside a case-sensitive table cannot be expressed by one fold, and that deployment-config knob is out of model; Self::Lower is the closest single fit and is what both dialects use. Per-identifier-kind casing is a deliberate future extension, gated on committing to a case-sensitive-table dialect (T-SQL): only then does the table-vs-column split change parse/identity results, so until such a dialect ships the added expressiveness would be unused surface (an M3 decision).

Variants

Upper

Fold unquoted identifiers to upper case (Oracle/DB2 style).

Lower

Fold unquoted identifiers to lower case (PostgreSQL style).

Preserve

Preserve unquoted identifier case as written (MySQL/SQL Server style).

Implementations

impl Casing

pub fn fold_identifier<'a>(&self, identifier: &'a str) -> Cow<'a, str>

Fold an unquoted identifier for dialect identity comparison.

M1 performs ASCII folding only. Non-ASCII bytes are preserved, matching the tokenizer’s permissive Unicode stance until a later precision pass introduces full Unicode identifier semantics.

Trait Implementations

impl Clone for Casing

fn clone(&self) -> Casing

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Casing

impl Debug for Casing

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

Formats the value using the given formatter.

impl Eq for Casing

impl PartialEq for Casing

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Casing