Function optimize_projections 

fn optimize_projections(
    plan: LogicalPlan,
    config: &dyn OptimizerConfig,
    indices: RequiredIndices,
) -> Result<Transformed<LogicalPlan>>

Removes unnecessary columns (e.g. columns that do not appear in the output schema and/or are not used during any computation step such as expression evaluation) from the logical plan and its inputs.

Parameters

• plan: A reference to the input LogicalPlan to optimize.
• config: A reference to the optimizer configuration.
• indices: A slice of column indices that represent the necessary column indices for downstream (parent) plan nodes.

Returns

A Result object with the following semantics:

• Ok(Some(LogicalPlan)): An optimized LogicalPlan without unnecessary columns.
• Ok(None): Signal that the given logical plan did not require any change.
• Err(error): An error occurred during the optimization process.