Constraint (Flink : 2.0-SNAPSHOT API)

All Known Implementing Classes:

UniqueConstraint
```
@PublicEvolving
public interface Constraint
```
Integrity constraints, generally referred to simply as constraints, define the valid states of SQL-data by constraining the values in the base tables.

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static class Constraint.ConstraintType
Type of the constraint.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`String`	`asSummaryString()`	Prints the constraint in a readable way.
`String`	`getName()`
`Constraint.ConstraintType`	`getType()`	Tells what kind of constraint it is, e.g.
`boolean`	`isEnforced()`	Constraints can either be enforced or non-enforced.

- Method Detail
  - getName
```
String getName()
```
  - isEnforced
```
boolean isEnforced()
```
    Constraints can either be enforced or non-enforced. If a constraint is enforced it will be checked whenever any SQL statement is executed that results in data or schema changes. If the constraint is not enforced the owner of the data is responsible for ensuring data integrity. Flink will rely the information is valid and might use it for query optimisations.
  - getType
```
Constraint.ConstraintType getType()
```
    Tells what kind of constraint it is, e.g. PRIMARY KEY, UNIQUE, ...
  - asSummaryString
```
String asSummaryString()
```
    Prints the constraint in a readable way.