Struct ExistenceGuards 

pub struct ExistenceGuards {
    pub if_exists: bool,
    pub view_if_not_exists: bool,
    pub create_database_if_not_exists: bool,
}

Dialect-owned IF [NOT] EXISTS existence guards on DDL statements.

The SQL existence guards — IF EXISTS on DROP/ALTER, IF NOT EXISTS on CREATE — are dialect data: each flag decides whether the parser admits the guard at one statement site, and when off the IF [NOT] EXISTS is left unconsumed and surfaces as a clean parse error (the same reject mechanism the other grammar gates use). They live in their own sub-struct rather than scattered through the retired SchemaChangeSyntax because their bundle membership differs per dialect: leaving a coarse if_exists bundle in SchemaChangeSyntax made every new dialect bolt on a separate exception flag (view_if_not_exists, create_database_if_not_exists), so a dedicated per-site table is the shape that does not accrete one exception per dialect.

Two-level spelling convention (uniform across the dialect-data knobs): a top-level FeatureSet assembly spells every field explicitly, while a sub-preset const of a knob like this one may struct-update-derive from a sibling with ..Self::OTHER (the SelectSyntax::DUCKDB precedent) — the base preset stays the exhaustive source of truth and the derived one records only its deltas.

Fields

if_exists: bool

Accept IF EXISTS on DROP/ALTER TABLE (and on their column/constraint sub-actions) and IF NOT EXISTS on ADD COLUMN (PostgreSQL, MySQL, SQLite; not ANSI, whose DROP/ALTER has no existence guard). One flag gates the drop/alter/add-column existence guards together because a dialect that spells one spells them all; the ALTER TABLE/ADD COLUMN sites additionally require IndexAlterSyntax::alter_table_extended (SQLite keeps this guard on for its DROP … IF EXISTS while its plain-ALTER surface stays off).

view_if_not_exists: bool

Accept IF NOT EXISTS on a plain (non-materialized) CREATE VIEW (SQLite). PostgreSQL admits IF NOT EXISTS only on a CREATE MATERIALIZED VIEW (that form is always accepted, independent of this flag), and MySQL has no view existence guard at all, so off there; SQLite spells CREATE VIEW IF NOT EXISTS over a regular view. When off, the IF NOT EXISTS is left unconsumed on a plain view and surfaces as a clean parse error.

create_database_if_not_exists: bool

Accept the CREATE DATABASE IF NOT EXISTS <name> existence guard (MySQL; also SQLite has no CREATE DATABASE at all, so off there). PostgreSQL’s CREATE DATABASE has no IF NOT EXISTS, so this is a dedicated site rather than a reuse of if_exists — that one is on in PostgreSQL, which must still reject CREATE DATABASE IF NOT EXISTS. When off, the IF NOT EXISTS is left unconsumed and surfaces as a clean parse error.

Implementations

impl ExistenceGuards

pub const ANSI: Self

The ANSI predefined value.

impl ExistenceGuards

pub const LENIENT: Self

Available on crate feature lenient only.

The LENIENT preset for existence guards.

impl ExistenceGuards

pub const MYSQL: Self

Available on crate feature mysql only.

The MYSQL preset for existence guards.

impl ExistenceGuards

pub const POSTGRES: Self

Available on crate feature postgres only.

The POSTGRES preset for existence guards.

impl ExistenceGuards

pub const SQLITE: Self

Available on crate feature sqlite only.

The SQLITE preset for existence guards.

Trait Implementations

impl Clone for ExistenceGuards

fn clone(&self) -> ExistenceGuards

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for ExistenceGuards

impl Debug for ExistenceGuards

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

Formats the value using the given formatter.

impl Eq for ExistenceGuards

impl PartialEq for ExistenceGuards

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for ExistenceGuards