Trait Dialect

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pub trait Dialect: Send + Sync {
    // Required methods
    fn capabilities(&self) -> BackendCapabilities;
    fn write_placeholder(&self, out: &mut String, index: usize);
    fn cast_type(&self, ty: SqlType) -> &'static str;

    // Provided methods
    fn write_ident(&self, out: &mut String, ident: &str) { ... }
    fn offset_requires_limit(&self) -> bool { ... }
    fn unbounded_limit(&self) -> &'static str { ... }
    fn like_escape_literal(&self) -> &'static str { ... }
    fn default_values_sql(&self) -> &'static str { ... }
    fn supports_aggregate_filter(&self) -> bool { ... }
    fn evaluates_assignments_in_order(&self) -> bool { ... }
}

Expand description

Differences between SQL flavours that the compiler needs to know about.

Required Methods§

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fn capabilities(&self) -> BackendCapabilities

Declared capabilities; the compiler rejects plans that exceed them.

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fn write_placeholder(&self, out: &mut String, index: usize)

Write the placeholder for the index-th (1-based) bind parameter.

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fn cast_type(&self, ty: SqlType) -> &'static str

Type name used in CAST(.. AS <name>).

Provided Methods§

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fn write_ident(&self, out: &mut String, ident: &str)

Write a quoted identifier. Embedded quote characters are doubled.

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fn offset_requires_limit(&self) -> bool

Whether OFFSET requires a preceding LIMIT.

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fn unbounded_limit(&self) -> &'static str

The LIMIT written before a bare OFFSET when offset_requires_limit is set.

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fn like_escape_literal(&self) -> &'static str

The SQL string literal used as the LIKE .. ESCAPE character (one backslash).

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fn default_values_sql(&self) -> &'static str

The tail of an INSERT INTO t that stores one row of defaults.

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fn supports_aggregate_filter(&self) -> bool

Whether aggregates accept FILTER (WHERE ..). When not, the compiler rewrites AGG(x) FILTER (WHERE f) as AGG(CASE WHEN f THEN x END).

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fn evaluates_assignments_in_order(&self) -> bool

Whether UPDATE .. SET a = .., b = .. evaluates the assignments left to right, so a later right-hand side sees the new value of an earlier column (standard SQL reads the old values). The compiler then reorders assignments to keep the standard meaning.