Package org.apache.calcite.rel

Class RelRoot

java.lang.Object
org.apache.calcite.rel.RelRoot
public class RelRoot extends Object
Root of a tree of RelNode.

One important reason that RelRoot exists is to deal with queries like

SELECT name FROM emp ORDER BY empno DESC

Calcite knows that the result must be sorted, but cannot represent its sort order as a collation, because empno is not a field in the result.

Instead we represent this as

RelRoot: { rel: Sort($1 DESC) Project(name, empno) TableScan(EMP) fields: [0] collation: [1 DESC] }

Note that the empno field is present in the result, but the fields mask tells the consumer to throw it away.

Another use case is queries like this:

SELECT name AS n, name AS n2, empno AS n FROM emp

The there are multiple uses of the name field. and there are multiple columns aliased as n. You can represent this as

RelRoot: { rel: Project(name, empno) TableScan(EMP) fields: [(0, "n"), (0, "n2"), (1, "n")] collation: [] }

  • Field Details

  • Constructor Details

  • Method Details

    • of

      public static RelRoot of(RelNode rel, SqlKind kind)
      Creates a simple RelRoot.

    • of

      public static RelRoot of(RelNode rel, RelDataType rowType, SqlKind kind)
      Creates a simple RelRoot.

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • withRel

      public RelRoot withRel(RelNode rel)
      Creates a copy of this RelRoot, assigning a RelNode.

    • withKind

      public RelRoot withKind(SqlKind kind)
      Creates a copy, assigning a new kind.

    • withCollation

      public RelRoot withCollation(RelCollation collation)

    • withHints

      public RelRoot withHints(List<RelHint> hints)
      Creates a copy, assigning the query hints.

    • project

      public RelNode project()
      Returns the root relational expression, creating a LogicalProject if necessary to remove fields that are not needed.

    • project

      public RelNode project(boolean force)
      Returns the root relational expression as a LogicalProject.
      Parameters:
      force - Create a Project even if all fields are used

    • isNameTrivial

      public boolean isNameTrivial()
      Returns true if the field names defined in this RelRoot are the same as the names of the embedded relation, otherwise false.

      Positive example (same names):

      RelRoot: { rel: Project(empno) TableScan(EMP) fields: [0 -> empno] collation: [] }

      Negative example (different names):

      RelRoot: { rel: Project(empno) TableScan(EMP) fields: [0 -> empid] collation: [] }
      Returns:
      true if the field names are the same as in the embedded relation, otherwise false

    • isRefTrivial

      public boolean isRefTrivial()
      Returns true if the embedded relation is either a DML relation or if the field order defined in this RelRoot is the same as the field order of the embedded relation, otherwise false.

      Positive example (same order):

      RelRoot: { rel: Project(name, empno) TableScan(EMP) fields: [0 -> name, 1 -> empno] collation: [] }

      Negative example (different order):

      RelRoot: { rel: Project(name, empno) TableScan(EMP) fields: [0 -> empno, 1 -> name] collation: [] }
      Returns:
      true if the embedded relation is a DML relation or if the field names of the RelRoot are in the same order as in the embedded relation, otherwise false

    • isCollationTrivial

      public boolean isCollationTrivial()
      Returns true if the embedded relation has a single collation defined which matches the collation of this RelRoot, otherwise false.
      Returns:
      true if the embedded relation has a single collation which matches the collation of this RelRoot, otherwise false