LogicalProperties (presto-spi 0.278 API)

```
public interface LogicalProperties
```
Logical properties represent constraints that hold for a final or intermediate result produced by a PlanNode. They are used by the optimizer to enable query transformations that lead to better performing plans. For example, unique constraints can be used to eliminate redundant distinct operations. This is the interface used by optimizer rules to perform optimizations based upon logical properties.
In this initial phase logical properties computed are based solely upon key constraints. In the future support for referential constraints, functional dependencies, and others will be added and hence this interface will become more robust over time.

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`boolean`	`isAtMost(long n)` Determines if there is provably at most n tuples in a final or intermediate result set produced by a PlanNode.
`boolean`	`isAtMostSingleRow()` Determines if there is provably at most one tuple in a final or intermediate result set produced by a PlanNode.
`boolean`	`isDistinct(Set<VariableReferenceExpression> keyVars)` Determines if the set of variables form a unique constraint for a final or intermediate result produced by a PlanNode.

Interface LogicalProperties