All Superinterfaces:

Cacheable

All Known Implementing Classes:

ExpressionVirtualColumn, FallbackVirtualColumn, ListFilteredVirtualColumn, NestedFieldVirtualColumn, SettableLongVirtualColumn
```
public interface VirtualColumn
extends Cacheable
```
Virtual columns are "views" created over a ColumnSelectorFactory or ColumnSelector. They can potentially draw from multiple underlying columns, although they always present themselves as if they were a single column. A virtual column object will be shared amongst threads and must be thread safe. The selectors returned from the various makeXXXSelector methods need not be thread safe.

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static interface VirtualColumn.EquivalenceKey

Method Summary

All Methods Instance Methods Abstract Methods Default Methods Deprecated Methods
Modifier and Type	Method	Description
`default boolean`	`canVectorize(ColumnInspector inspector)`
`ColumnCapabilities`	`capabilities(String columnName)`	Deprecated.
`default ColumnCapabilities`	`capabilities(ColumnInspector inspector, String columnName)`	Return the `ColumnCapabilities` which best describe the optimal selector to read from this virtual column.
`default VirtualColumn.EquivalenceKey`	`getEquivalanceKey()`	Returns a key used for "equivalence" comparisons, for checking if some virtual column is equivalent to some other virtual column, regardless of the output name.
`default ColumnIndexSupplier`	`getIndexSupplier(String columnName, ColumnIndexSelector columnIndexSelector)`	Get the `ColumnIndexSupplier` for the specified virtual column, with the assistance of a `ColumnIndexSelector` to allow reading things from segments.
`String`	`getOutputName()`	Output name of this column.
`ColumnValueSelector<?>`	`makeColumnValueSelector(String columnName, ColumnSelectorFactory factory)`	Build a `ColumnValueSelector` corresponding to this virtual column.
`default ColumnValueSelector<?>`	`makeColumnValueSelector(String columnName, ColumnSelector columnSelector, ReadableOffset offset)`	Returns similar `ColumnValueSelector` object as returned by `makeColumnValueSelector(String, ColumnSelectorFactory)` except this method has full access to the underlying column and can potentially provide a more efficient implementation.
`DimensionSelector`	`makeDimensionSelector(DimensionSpec dimensionSpec, ColumnSelectorFactory factory)`	Build a selector corresponding to this virtual column.
`default DimensionSelector`	`makeDimensionSelector(DimensionSpec dimensionSpec, ColumnSelector columnSelector, ReadableOffset offset)`	Returns similar `DimensionSelector` object as returned by `makeDimensionSelector(DimensionSpec, ColumnSelectorFactory)` except this method has full access to the underlying column and can potentially provide a more efficient implementation.
`default GroupByVectorColumnSelector`	`makeGroupByVectorColumnSelector(String columnName, VectorColumnSelectorFactory factory, DeferExpressionDimensions deferExpressionDimensions)`	Returns a group-by selector.
`default MultiValueDimensionVectorSelector`	`makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec, ColumnSelector columnSelector, ReadableVectorOffset offset)`	Returns similar `SingleValueDimensionVectorSelector` object as returned by `makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset)` except this method has full access to the underlying column and can potentially provide a more efficient implementation.
`default MultiValueDimensionVectorSelector`	`makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec, VectorColumnSelectorFactory factory)`	Build a `MultiValueDimensionVectorSelector` corresponding to this virtual column.
`default SingleValueDimensionVectorSelector`	`makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec, ColumnSelector columnSelector, ReadableVectorOffset offset)`	Returns similar `SingleValueDimensionVectorSelector` object as returned by `makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset)` except this method has full access to the underlying column and can potentially provide a more efficient implementation.
`default SingleValueDimensionVectorSelector`	`makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec, VectorColumnSelectorFactory factory)`	Build a `SingleValueDimensionVectorSelector` corresponding to this virtual column.
`default VectorObjectSelector`	`makeVectorObjectSelector(String columnName, ColumnSelector columnSelector, ReadableVectorOffset offset)`	Returns similar `VectorObjectSelector` object as returned by `makeVectorObjectSelector(String, VectorColumnSelectorFactory)` except this method has full access to the underlying column and can potentially provide a more efficient implementation.
`default VectorObjectSelector`	`makeVectorObjectSelector(String columnName, VectorColumnSelectorFactory factory)`	Build a `VectorObjectSelector` corresponding to this virtual column.
`default VectorValueSelector`	`makeVectorValueSelector(String columnName, ColumnSelector columnSelector, ReadableVectorOffset offset)`	Returns similar `VectorValueSelector` object as returned by `makeVectorValueSelector(String, VectorColumnSelectorFactory)` except this method has full access to the underlying column and can potentially provide a more efficient implementation.
`default VectorValueSelector`	`makeVectorValueSelector(String columnName, VectorColumnSelectorFactory factory)`	Build a `VectorValueSelector` corresponding to this virtual column.
`List<String>`	`requiredColumns()`	Returns a list of columns that this virtual column will access.
`boolean`	`usesDotNotation()`	Indicates that this virtual column can be referenced with dot notation.

Methods inherited from interface org.apache.druid.java.util.common.Cacheable
getCacheKey

- Method Detail
  - getOutputName
```
String getOutputName()
```
    Output name of this column.
    
    Returns:
    
    name
  - makeDimensionSelector
```
DimensionSelector makeDimensionSelector(DimensionSpec dimensionSpec,
                                        ColumnSelectorFactory factory)
```
    Build a selector corresponding to this virtual column. Also provides the name that the virtual column was referenced with (through DimensionSpec.getDimension(), which is useful if this column uses dot notation. The virtual column is expected to apply any necessary decoration from the dimensionSpec.
  - makeDimensionSelector
```
@Nullable
default DimensionSelector makeDimensionSelector(DimensionSpec dimensionSpec,
                                                ColumnSelector columnSelector,
                                                ReadableOffset offset)
```
    Returns similar DimensionSelector object as returned by makeDimensionSelector(DimensionSpec, ColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible. Typically this can not be called in query paths on top of IncrementalIndex which doesn't have columns as in persisted segments.
  - makeColumnValueSelector
```
ColumnValueSelector<?> makeColumnValueSelector(String columnName,
                                               ColumnSelectorFactory factory)
```
    Build a ColumnValueSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with, which is useful if this column uses dot notation.
  - makeColumnValueSelector
```
@Nullable
default ColumnValueSelector<?> makeColumnValueSelector(String columnName,
                                                       ColumnSelector columnSelector,
                                                       ReadableOffset offset)
```
    Returns similar ColumnValueSelector object as returned by makeColumnValueSelector(String, ColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible. Typically this can not be called in query paths on top of IncrementalIndex which doesn't have columns as in persisted segments.
  - canVectorize
```
default boolean canVectorize(ColumnInspector inspector)
```
  - makeSingleValueVectorDimensionSelector
```
default SingleValueDimensionVectorSelector makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                  VectorColumnSelectorFactory factory)
```
    Build a SingleValueDimensionVectorSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with (through DimensionSpec.getDimension(), which is useful if this column uses dot notation. The virtual column is expected to apply any necessary decoration from the DimensionSpec.
  - makeSingleValueVectorDimensionSelector
```
@Nullable
default SingleValueDimensionVectorSelector makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                  ColumnSelector columnSelector,
                                                                                  ReadableVectorOffset offset)
```
    Returns similar SingleValueDimensionVectorSelector object as returned by makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.
  - makeMultiValueVectorDimensionSelector
```
default MultiValueDimensionVectorSelector makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                VectorColumnSelectorFactory factory)
```
    Build a MultiValueDimensionVectorSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with (through DimensionSpec.getDimension(), which is useful if this column uses dot notation. The virtual column is expected to apply any necessary decoration from the DimensionSpec.
  - makeMultiValueVectorDimensionSelector
```
@Nullable
default MultiValueDimensionVectorSelector makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                ColumnSelector columnSelector,
                                                                                ReadableVectorOffset offset)
```
    Returns similar SingleValueDimensionVectorSelector object as returned by makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.
  - makeVectorValueSelector
```
default VectorValueSelector makeVectorValueSelector(String columnName,
                                                    VectorColumnSelectorFactory factory)
```
    Build a VectorValueSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with, which is useful if this column uses dot notation.
  - makeVectorValueSelector
```
@Nullable
default VectorValueSelector makeVectorValueSelector(String columnName,
                                                    ColumnSelector columnSelector,
                                                    ReadableVectorOffset offset)
```
    Returns similar VectorValueSelector object as returned by makeVectorValueSelector(String, VectorColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.
  - makeVectorObjectSelector
```
default VectorObjectSelector makeVectorObjectSelector(String columnName,
                                                      VectorColumnSelectorFactory factory)
```
    Build a VectorObjectSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with, which is useful if this column uses dot notation.
  - makeVectorObjectSelector
```
@Nullable
default VectorObjectSelector makeVectorObjectSelector(String columnName,
                                                      ColumnSelector columnSelector,
                                                      ReadableVectorOffset offset)
```
    Returns similar VectorObjectSelector object as returned by makeVectorObjectSelector(String, VectorColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.
  - makeGroupByVectorColumnSelector
```
@Nullable
default GroupByVectorColumnSelector makeGroupByVectorColumnSelector(String columnName,
                                                                    VectorColumnSelectorFactory factory,
                                                                    DeferExpressionDimensions deferExpressionDimensions)
```
    Returns a group-by selector. Allows virtual columns to control their own grouping behavior.
    
    Parameters:
    
    columnName - column name
    
    factory - column selector factory
    
    deferExpressionDimensions - active value of GroupByQueryConfig.CTX_KEY_DEFER_EXPRESSION_DIMENSIONS
    
    Returns:
    
    selector, or null if this virtual column does not have a specialized one
  - capabilities
```
@Deprecated
ColumnCapabilities capabilities(String columnName)
```
    Deprecated.
    
    This method is deprecated in favor of capabilities(ColumnInspector, String), which should be used whenever possible and can support virtual column implementations that need to inspect other columns as inputs. This is a fallback implementation to return the capabilities of this virtual column, which includes a type that corresponds to the best performing base selector supertype (e. g. BaseLongColumnValueSelector) of the object, returned from makeColumnValueSelector(String, ColumnSelectorFactory). May vary based on columnName if this column uses dot notation.
    
    Parameters:
    
    columnName - the name this virtual column was referenced with
    
    Returns:
    
    capabilities, must not be null
  - capabilities
```
@Nullable
default ColumnCapabilities capabilities(ColumnInspector inspector,
                                        String columnName)
```
    Return the ColumnCapabilities which best describe the optimal selector to read from this virtual column.
    The ColumnInspector (most likely corresponding to an underlying ColumnSelectorFactory of a query) allows the virtual column to consider this information if necessary to compute its output type details.
    Examples of this include the ExpressionVirtualColumn, which takes input from other columns and uses the ColumnInspector to infer the output type of expressions based on the types of the inputs.
    
    Parameters:
    
    inspector - column inspector to provide additional information of other available columns
    
    columnName - the name this virtual column was referenced with
    
    Returns:
    
    capabilities, must not be null
  - requiredColumns
```
List<String> requiredColumns()
```
    Returns a list of columns that this virtual column will access. This may include the names of other virtual columns. May be empty if a virtual column doesn't access any underlying columns. Does not pass columnName because there is an assumption that the list of columns needed by a dot-notation supporting virtual column will not vary based on the columnName.
    
    Returns:
    
    column names
  - usesDotNotation
```
boolean usesDotNotation()
```
    Indicates that this virtual column can be referenced with dot notation. For example, a virtual column named "foo" could be referred to as "foo.bar" with the Cursor it is registered with. In that case, init will be called with columnName "foo.bar" rather than "foo".
    
    Returns:
    
    whether to use dot notation
  - getIndexSupplier
```
@Nullable
default ColumnIndexSupplier getIndexSupplier(String columnName,
                                             ColumnIndexSelector columnIndexSelector)
```
    Get the ColumnIndexSupplier for the specified virtual column, with the assistance of a ColumnIndexSelector to allow reading things from segments. If the virtual column has no indexes, this method will return null, or may also return a non-null supplier whose methods may return null values - having a supplier is no guarantee that the column has indexes.
  - getEquivalanceKey
```
@Nullable
default VirtualColumn.EquivalenceKey getEquivalanceKey()
```
    Returns a key used for "equivalence" comparisons, for checking if some virtual column is equivalent to some other virtual column, regardless of the output name. If this method returns null, it does not participate in equivalence comparisons.
    
    See Also:
    
    VirtualColumns.findEquivalent(VirtualColumn)

Interface VirtualColumn

Nested Class Summary

Method Summary

Methods inherited from interface org.apache.druid.java.util.common.Cacheable

Method Detail

getOutputName

makeDimensionSelector

makeDimensionSelector

makeColumnValueSelector

makeColumnValueSelector

canVectorize

makeSingleValueVectorDimensionSelector

makeSingleValueVectorDimensionSelector

makeMultiValueVectorDimensionSelector

makeMultiValueVectorDimensionSelector

makeVectorValueSelector

makeVectorValueSelector

makeVectorObjectSelector

makeVectorObjectSelector

makeGroupByVectorColumnSelector

capabilities

capabilities

requiredColumns

usesDotNotation

getIndexSupplier

getEquivalanceKey