Module projection 

Defines the projection execution plan. A projection determines which columns or expressions are returned from a query. The SQL statement SELECT a, b, a+b FROM t1 is an example of a projection on table t1 where the expressions a, b, and a+b are the projection expressions. SELECT without FROM will only evaluate expressions.

Structs

JoinData

ProjectionExec

ExecutionPlan for a projection

ProjectionExpr

A projection expression as used by projection operations.

ProjectionExprs

A collection of projection expressions.

ProjectionStream 🔒

Projection iterator

Traits

EmbeddedProjection

Functions

all_alias_free_columns

Given the expression set of a projection, checks if the projection causes any renaming or constructs a non-Column physical expression.

all_columns

Returns true if all the expressions in the argument are Columns.

collect_column_indices 🔒

Collect all column indices from the given projection expressions.

is_expr_trivial 🔒

Checks if the given expression is trivial. An expression is considered trivial if it is either a Column or a Literal.

is_projection_removable 🔒

Compare the inputs and outputs of the projection. All expressions must be columns without alias, and projection does not change the order of fields. For example, if the input schema is a, b, SELECT a, b is removable, but SELECT b, a and SELECT a+1, b and SELECT a AS c, b are not.

join_allows_pushdown

Checks three conditions for pushing a projection down through a join:

join_table_borders

Returns the last index before encountering a column coming from the right table when traveling through the projection from left to right, and the last index before encountering a column coming from the left table when traveling through the projection from right to left. If there is no column in the projection coming from the left side, it returns (-1, …), if there is no column in the projection coming from the right side, it returns (…, projection length).

make_with_child

Creates a new ProjectionExec instance with the given child plan and projected expressions.

new_columns_for_join_on 🔒

This function generates a new set of columns to be used in a hash join operation based on a set of equi-join conditions (hash_join_on) and a list of projection expressions (projection_exprs).

new_indices_for_join_filter 🔒

This function determines and returns a vector of indices representing the positions of columns in projection_exprs that are involved in join_filter, and correspond to a particular side (join_side) of the join operation.

new_join_children

If pushing down the projection over this join’s children seems possible, this function constructs the new ProjectionExecs that will come on top of the original children of the join.

new_projections_for_columns

Updates a source provider’s projected columns according to the given projection operator’s expressions. To use this function safely, one must ensure that all expressions are Column expressions without aliases.

physical_to_column_exprs

Downcasts all the expressions in exprs to Columns. If any of the given expressions is not a Column, returns None.

remove_unnecessary_projections

This function checks if plan is a ProjectionExec, and inspects its input(s) to test whether it can push plan under its input(s). This function will operate on the entire tree and may ultimately remove plan entirely by leveraging source providers with built-in projection capabilities.

try_embed_projection

Some projection can’t be pushed down left input or right input of hash join because filter or on need may need some columns that won’t be used in later. By embed those projection to hash join, we can reduce the cost of build_batch_from_indices in hash join (build_batch_from_indices need to can compute::take() for each column) and avoid unnecessary output creation.

try_pushdown_through_join

try_unifying_projections 🔒

Unifies projection with its input (which is also a ProjectionExec).

update_expr

The function operates in two modes:

update_join_filter

Tries to update the column indices of a JoinFilter as if the input of the join was replaced by a projection.

update_join_on

Tries to update the equi-join Column’s of a join as if the input of the join was replaced by a projection.

update_ordering

Updates the given lexicographic ordering according to given projected expressions using the update_expr function.

update_ordering_requirement

Updates the given lexicographic requirement according to given projected expressions using the update_expr function.