Function update_expr 

pub fn update_expr(
    expr: &Arc<dyn PhysicalExpr>,
    projected_exprs: &[ProjectionExpr],
    unproject: bool,
) -> Result<Option<Arc<dyn PhysicalExpr>>>

The function projects / unprojects an expression with respect to set of projection expressions.

See also ProjectionExprs::unproject_expr and ProjectionExprs::project_expr

1. When unproject is true:

   Rewrites an expression with respect to the projection expressions, effectively “unprojecting” it to reference the original input columns.

   For example, given

   • the expressions a@1 + b@2 and c@0
   • and projection expressions c@2, a@0, b@1

   Then

   • a@1 + b@2 becomes a@0 + b@1
   • c@0 becomes c@2

2. When unproject is false:

   Rewrites the expression to reference the projected expressions, effectively “projecting” it. The resulting expression will reference the indices as they appear in the projection.

   If the expression cannot be rewritten after the projection, it returns None.

   For example, given

   • the expressions c@0, a@1 and b@2
   • the projection a@1 as a, c@0 as c_new,

   Then

   • c@0 becomes c_new@1
   • a@1 becomes a@0
   • b@2 results in None since the projection does not include b.

Errors

This function returns an error if unproject is true and if any expression references an index that is out of bounds for projected_exprs. For example:

• expr is a@3
• projected_exprs is [a@0, b@1]

In this case, a@3 references index 3, which is out of bounds for projected_exprs (which has length 2).