Package org.apache.drill.exec.physical.impl.scan.project

Enum ScanLevelProjection.ScanProjectionType

java.lang.Object
java.lang.Enum<ScanLevelProjection.ScanProjectionType>
org.apache.drill.exec.physical.impl.scan.project.ScanLevelProjection.ScanProjectionType
All Implemented Interfaces:
Serializable, Comparable<ScanLevelProjection.ScanProjectionType>
Enclosing class:
ScanLevelProjection
public static enum ScanLevelProjection.ScanProjectionType extends Enum<ScanLevelProjection.ScanProjectionType>
Identifies the kind of projection done for this scan.

  • Enum Constant Details

    • EMPTY

      public static final ScanLevelProjection.ScanProjectionType EMPTY
      No projection. Occurs for SELECT COUNT(*) ... queries.

    • WILDCARD

      public static final ScanLevelProjection.ScanProjectionType WILDCARD
      Wildcard. Occurs for SELECT * ... queries when no output schema is available. The scan projects all columns from all readers, using the type from that reader. Schema "smoothing", if enabled, will attempt to preserve column order, type and mode from one reader to the next.

    • EXPLICIT

      public static final ScanLevelProjection.ScanProjectionType EXPLICIT
      Explicit projection. Occurs for SELECT a, b, c ... queries, whether or not an output schema is present. In this case, the projection list identifies the set of columns to project and their order. The output schema, if present, specifies data types and modes.

    • SCHEMA_WILDCARD

      public static final ScanLevelProjection.ScanProjectionType SCHEMA_WILDCARD
      Wildcard query expanded using an output schema. Occurs for a SELECT * ... query with an output schema. The set of projected columns are those from the output schema, in the order specified by the schema, with names (and name case) specified by the schema. In this mode, the schema is partial: readers may include additional columns which are appended to those provided by the schema.

      TODO: Provide a strict mode that forces the use of the types and modes from the output schema. In lenient mode, the framework will adjust mode to allow the query to succeed (changing a required mode to optional, say, if the column is not provided by the reader and has no default. Strict mode would fail the query in this case.)

      TODO: Enable schema smoothing in this case: use that mechanism to smooth over the "extra" reader columns.

    • STRICT_SCHEMA_WILDCARD

      public static final ScanLevelProjection.ScanProjectionType STRICT_SCHEMA_WILDCARD
      Wildcard query expanded using an output schema in "strict" mode. Only columns from the output schema will be projected. If a reader offers columns not in the output schema, they will be ignored. That is, a SELECT * query expands to exactly the columns in the schema.

      TODO: Provide a strict column mode that will fail the query if a projected column is required, has no default, and is not provided by the reader. In the normal lenient mode, the scan framework will adjust the data mode to optional so that the query will run.

  • Method Details

    • values

      public static ScanLevelProjection.ScanProjectionType[] values()
      Returns an array containing the constants of this enum type, in the order they are declared.
      Returns:
      an array containing the constants of this enum type, in the order they are declared

    • valueOf

      public static ScanLevelProjection.ScanProjectionType valueOf(String name)
      Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)
      Parameters:
      name - the name of the enum constant to be returned.
      Returns:
      the enum constant with the specified name
      Throws:
      IllegalArgumentException - if this enum type has no constant with the specified name
      NullPointerException - if the argument is null

    • isWildcard

      public boolean isWildcard()