All Superinterfaces:

TypeSignature<ValueType>

All Known Implementing Classes:

ColumnCapabilitiesImpl
```
public interface ColumnCapabilities
extends TypeSignature<ValueType>
```
This interface is used to expose information about columns that is interesting to know for all matters dealing with reading from columns, including query planning and optimization, creating readers to merge segments at ingestion time, and probably nearly anything else you can imagine.

See Also:

ColumnType, TypeSignature

Nested Class Summary

Nested Classes
Modifier and Type	Interface	Description
`static class`	`ColumnCapabilities.Capable`
`static interface`	`ColumnCapabilities.CoercionLogic`	This interface defines the shape of a mechnism to allow for bespoke coercion of `ColumnCapabilities.Capable.UNKNOWN` into `ColumnCapabilities.Capable.TRUE` or `ColumnCapabilities.Capable.FALSE` for each `ColumnCapabilities.Capable` of a `ColumnCapabilities`, as is appropriate for the situation of the caller.

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`ColumnCapabilities.Capable`	`areDictionaryValuesSorted()`	If the column is dictionary encoded, are those values sorted? Useful to know for optimizations that can defer looking up values and allowing sorting with the dictionary ids directly
`ColumnCapabilities.Capable`	`areDictionaryValuesUnique()`	If the column is dictionary encoded, is there a 1:1 mapping of dictionary ids to values? If this is true, it unlocks optimizations such as allowing for things like grouping directly on dictionary ids and deferred value lookup
`default <T> TypeStrategy<T>`	`getStrategy()`	A `TypeStrategy` provides facilities to reading and writing values to buffers, as well as basic value comparators and byte size estimation.
`boolean`	`hasBitmapIndexes()`	Does the column have an inverted index bitmap for each value? If so, these may be employed to 'pre-filter' the column by examining if the values match the filter and intersecting the bitmaps, to avoid having to scan and evaluate if every row matches the filter
`ColumnCapabilities.Capable`	`hasMultipleValues()`	String columns are sneaky, and might have multiple values, this is to allow callers to know and appropriately prepare themselves
`ColumnCapabilities.Capable`	`hasNulls()`	Does this column contain null values? If so, callers, especially for primitive numeric columns, will need to check for null value rows and act accordingly
`boolean`	`hasSpatialIndexes()`	Does the column have spatial indexes available to allow use with spatial filtering?
`ColumnCapabilities.Capable`	`isDictionaryEncoded()`	Is the column dictionary encoded? If so, a DimensionDictionarySelector may be used instead of using a value selector, allowing algorithms to operate on primitive integer dictionary ids rather than the looked up dictionary values
`default ColumnType`	`toColumnType()`

Methods inherited from interface org.apache.druid.segment.column.TypeSignature
anyOf, asTypeString, getComplexTypeName, getElementType, getNullableStrategy, getType, is, isArray, isNumeric, isPrimitive, isPrimitiveArray

- Method Detail
  - isDictionaryEncoded
```
ColumnCapabilities.Capable isDictionaryEncoded()
```
    Is the column dictionary encoded? If so, a DimensionDictionarySelector may be used instead of using a value selector, allowing algorithms to operate on primitive integer dictionary ids rather than the looked up dictionary values
  - areDictionaryValuesSorted
```
ColumnCapabilities.Capable areDictionaryValuesSorted()
```
    If the column is dictionary encoded, are those values sorted? Useful to know for optimizations that can defer looking up values and allowing sorting with the dictionary ids directly
  - areDictionaryValuesUnique
```
ColumnCapabilities.Capable areDictionaryValuesUnique()
```
    If the column is dictionary encoded, is there a 1:1 mapping of dictionary ids to values? If this is true, it unlocks optimizations such as allowing for things like grouping directly on dictionary ids and deferred value lookup
  - hasMultipleValues
```
ColumnCapabilities.Capable hasMultipleValues()
```
    String columns are sneaky, and might have multiple values, this is to allow callers to know and appropriately prepare themselves
  - hasBitmapIndexes
```
boolean hasBitmapIndexes()
```
    Does the column have an inverted index bitmap for each value? If so, these may be employed to 'pre-filter' the column by examining if the values match the filter and intersecting the bitmaps, to avoid having to scan and evaluate if every row matches the filter
  - hasSpatialIndexes
```
boolean hasSpatialIndexes()
```
    Does the column have spatial indexes available to allow use with spatial filtering?
  - hasNulls
```
ColumnCapabilities.Capable hasNulls()
```
    Does this column contain null values? If so, callers, especially for primitive numeric columns, will need to check for null value rows and act accordingly
  - toColumnType
```
default ColumnType toColumnType()
```
  - getStrategy
```
default <T> TypeStrategy<T> getStrategy()
```
    Description copied from interface: TypeSignature
    
    A TypeStrategy provides facilities to reading and writing values to buffers, as well as basic value comparators and byte size estimation. Use TypeSignature.getNullableStrategy() if you need to read and write values which might possibly be null and aren't handling this in a different (probably better) way.
    
    Specified by:
    
    getStrategy in interface TypeSignature<ValueType>

Interface ColumnCapabilities

Nested Class Summary

Method Summary

Methods inherited from interface org.apache.druid.segment.column.TypeSignature

Method Detail

isDictionaryEncoded

areDictionaryValuesSorted

areDictionaryValuesUnique

hasMultipleValues

hasBitmapIndexes

hasSpatialIndexes

hasNulls

toColumnType

getStrategy