pub trait Transform: Send + Sync {
// Required methods
fn name(&self) -> String;
fn get_reduction_points(&self, ast: Statement) -> Vec<usize>;
fn apply_on(
&self,
ast: &mut Statement,
reduction_points: Vec<usize>,
) -> Statement;
// Provided method
fn transform(
&self,
ast: Statement,
idx: usize,
strategy: Strategy,
) -> Vec<(Statement, usize)> { ... }
}Expand description
A transformation that can reduce parts of a SQL AST while preserving failure behavior.
A Transform operates by identifying reduction points in the AST—locations where
a simplification or mutation can be safely attempted—and then applying those changes.
§Reduction Points
A reduction point is an index identifying a target element (e.g., a SELECT item, a WHERE clause, or a binary operator) that can be removed, replaced, or mutated.
§Example:
- For a
SELECTlist:SELECT a + b, c, d FROM t; ^ ^ | └── reduction point 1 (c) └────── reduction point 0 (a + b)
Required Methods§
fn name(&self) -> String
Sourcefn get_reduction_points(&self, ast: Statement) -> Vec<usize>
fn get_reduction_points(&self, ast: Statement) -> Vec<usize>
This function analyzes the given SQL AST and returns all the reduction points where the transformation might be applicable.
§Arguments
ast: The SQL AST to analyze.
§Returns
- A list of reduction points where the transformation might be applicable.
Implementors should return a list of all applicable reduction indices for their transform.
Provided Methods§
Sourcefn transform(
&self,
ast: Statement,
idx: usize,
strategy: Strategy,
) -> Vec<(Statement, usize)>
fn transform( &self, ast: Statement, idx: usize, strategy: Strategy, ) -> Vec<(Statement, usize)>
Applies the transformation to the AST at the given reduction points.
§Arguments
ast: The SQL AST to apply the transformation to.idx: The index of the reduction point to apply the transformation to.strategy: The strategy to use for applying the transformation.