mz_expr::scalar::func::binary

Trait LazyBinaryFunc

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pub(crate) trait LazyBinaryFunc {
    // Required methods
    fn eval<'a>(
        &'a self,
        datums: &[Datum<'a>],
        temp_storage: &'a RowArena,
        a: &'a MirScalarExpr,
        b: &'a MirScalarExpr,
    ) -> Result<Datum<'a>, EvalError>;
    fn output_type(
        &self,
        input_type_a: ColumnType,
        input_type_b: ColumnType,
    ) -> ColumnType;
    fn propagates_nulls(&self) -> bool;
    fn introduces_nulls(&self) -> bool;
    fn negate(&self) -> Option<BinaryFunc>;
    fn is_monotone(&self) -> (bool, bool);
    fn is_infix_op(&self) -> bool;

    // Provided method
    fn could_error(&self) -> bool { ... }
}

Expand description

A description of an SQL binary function that has the ability to lazy evaluate its arguments

Required Methods§

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fn eval<'a>( &'a self, datums: &[Datum<'a>], temp_storage: &'a RowArena, a: &'a MirScalarExpr, b: &'a MirScalarExpr, ) -> Result<Datum<'a>, EvalError>

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fn output_type( &self, input_type_a: ColumnType, input_type_b: ColumnType, ) -> ColumnType

The output ColumnType of this function.

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fn propagates_nulls(&self) -> bool

Whether this function will produce NULL on NULL input.

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fn introduces_nulls(&self) -> bool

Whether this function will produce NULL on non-NULL input.

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fn negate(&self) -> Option<BinaryFunc>

Returns the negation of the function, if one exists.

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fn is_monotone(&self) -> (bool, bool)

Returns true if the function is monotone. (Non-strict; either increasing or decreasing.) Monotone functions map ranges to ranges: ie. given a range of possible inputs, we can determine the range of possible outputs just by mapping the endpoints.

This describes the pointwise behaviour of the function: ie. the behaviour of any specific argument as the others are held constant. (For example, a - b is monotone in the first argument because for any particular value of b, increasing a will always cause the result to increase… and in the second argument because for any specific a, increasing b will always cause the result to decrease.)

This property describes the behaviour of the function over ranges where the function is defined: ie. the arguments and the result are non-error datums.

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