Interface Dialect

datafusion/sql/src/unparser/dialect.rs:50–294

`Dialect` to use for Unparsing The default dialect tries to avoid quoting identifiers unless necessary (e.g. `a` instead of `"a"`) but this behavior can be overridden as needed Note**: This trait will eventually be replaced by the Dialect in the SQLparser package See See also the discussion in <https://github.com/apache/datafusion/pull/10

/// See <https://github.com/sqlparser-rs/sqlparser-rs/pull/1170>
/// See also the discussion in <https://github.com/apache/datafusion/pull/10625>
pub trait Dialect: Send + Sync {
    /// Return the character used to quote identifiers.
    fn identifier_quote_style(&self, _identifier: &str) -> Option<char>;

    /// Whether array literals should be rendered with the `ARRAY[...]` keyword.
    fn use_array_keyword_for_array_literals(&self) -> bool {
        false
    }

    /// Does the dialect support specifying `NULLS FIRST/LAST` in `ORDER BY` clauses?
    fn supports_nulls_first_in_sort(&self) -> bool {
        true
    }

    /// Does the dialect use TIMESTAMP to represent Date64 rather than DATETIME?
    /// E.g. Trino, Athena and Dremio does not have DATETIME data type
    fn use_timestamp_for_date64(&self) -> bool {
        false
    }

    fn interval_style(&self) -> IntervalStyle {
        IntervalStyle::PostgresVerbose
    }

    /// Does the dialect use DOUBLE PRECISION to represent Float64 rather than DOUBLE?
    /// E.g. Postgres uses DOUBLE PRECISION instead of DOUBLE
    fn float64_ast_dtype(&self) -> ast::DataType {
        ast::DataType::Double(ast::ExactNumberInfo::None)
    }

    /// The SQL type to use for Arrow Utf8 unparsing
    /// Most dialects use VARCHAR, but some, like MySQL, require CHAR
    fn utf8_cast_dtype(&self) -> ast::DataType {
        ast::DataType::Varchar(None)
    }

    /// The SQL type to use for Arrow LargeUtf8 unparsing
    /// Most dialects use TEXT, but some, like MySQL, require CHAR
    fn large_utf8_cast_dtype(&self) -> ast::DataType {
        ast::DataType::Text
    }

    /// The date field extract style to use: `DateFieldExtractStyle`
    fn date_field_extract_style(&self) -> DateFieldExtractStyle {
        DateFieldExtractStyle::DatePart
    }

    /// The character length extraction style to use: `CharacterLengthStyle`
    fn character_length_style(&self) -> CharacterLengthStyle {
        CharacterLengthStyle::CharacterLength
    }

    /// The SQL type to use for Arrow Int64 unparsing
    /// Most dialects use BigInt, but some, like MySQL, require SIGNED
    fn int64_cast_dtype(&self) -> ast::DataType {
        ast::DataType::BigInt(None)
    }