Schema (Flink : Table : Common 2.0-preview1 API)

java.lang.Object
- org.apache.flink.table.api.Schema

```
@PublicEvolving
public final class Schema
extends Object
```
Schema of a table or view.
A schema represents the schema part of a CREATE TABLE (schema) WITH (options) DDL statement in SQL. It defines columns of different kind, constraints, time attributes, and watermark strategies. It is possible to reference objects (such as functions or types) across different catalogs.
This class is used in the API and catalogs to define an unresolved schema that will be translated to ResolvedSchema. Some methods of this class perform basic validation, however, the main validation happens during the resolution. Thus, an unresolved schema can be incomplete and might be enriched or merged with a different schema at a later stage.
Since an instance of this class is unresolved, it should not be directly persisted. The toString() shows only a summary of the contained objects.

Nested Class Summary

Nested Classes
Modifier and Type	Class	Description
`static class`	`Schema.Builder`	A builder for constructing an immutable but still unresolved `Schema`.
`static class`	`Schema.UnresolvedColumn`	Super class for all kinds of columns in an unresolved schema.
`static class`	`Schema.UnresolvedComputedColumn`	Declaration of a computed column that will be resolved to `Column.ComputedColumn` during schema resolution.
`static class`	`Schema.UnresolvedConstraint`	Super class for all kinds of constraints in an unresolved schema.
`static class`	`Schema.UnresolvedMetadataColumn`	Declaration of a metadata column that will be resolved to `Column.MetadataColumn` during schema resolution.
`static class`	`Schema.UnresolvedPhysicalColumn`	Declaration of a physical column that will be resolved to `Column.PhysicalColumn` during schema resolution.
`static class`	`Schema.UnresolvedPrimaryKey`	Declaration of a primary key that will be resolved to `UniqueConstraint` during schema resolution.
`static class`	`Schema.UnresolvedWatermarkSpec`	Declaration of a watermark strategy that will be resolved to `WatermarkSpec` during schema resolution.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`static Schema`	`derived()`	Convenience method for stating explicitly that a schema is empty and should be fully derived by the framework.
`boolean`	`equals(Object o)`
`List<Schema.UnresolvedColumn>`	`getColumns()`
`Optional<Schema.UnresolvedPrimaryKey>`	`getPrimaryKey()`
`List<Schema.UnresolvedWatermarkSpec>`	`getWatermarkSpecs()`
`int`	`hashCode()`
`static Schema.Builder`	`newBuilder()`	Builder for configuring and creating instances of `Schema`.
`ResolvedSchema`	`resolve(SchemaResolver resolver)`	Resolves the given `Schema` to a validated `ResolvedSchema`.
`String`	`toString()`

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Method Detail
  - newBuilder
```
public static Schema.Builder newBuilder()
```
    Builder for configuring and creating instances of Schema.
  - derived
```
public static Schema derived()
```
    Convenience method for stating explicitly that a schema is empty and should be fully derived by the framework.
    The semantics are equivalent to calling Schema.newBuilder().build().
    Note that derivation depends on the context. Usually, the method that accepts a Schema instance will mention whether schema derivation is supported or not.
  - getColumns
```
public List<Schema.UnresolvedColumn> getColumns()
```
  - getWatermarkSpecs
```
public List<Schema.UnresolvedWatermarkSpec> getWatermarkSpecs()
```
  - getPrimaryKey
```
public Optional<Schema.UnresolvedPrimaryKey> getPrimaryKey()
```
  - resolve
```
public ResolvedSchema resolve(SchemaResolver resolver)
```
    Resolves the given Schema to a validated ResolvedSchema.
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object
  - equals
```
public boolean equals(Object o)
```
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object