SubqueryOperator (NanoDB SQL Relational Database 0.1-SNAPSHOT API)

java.lang.Object
- edu.caltech.nanodb.expressions.Expression
- - edu.caltech.nanodb.expressions.SubqueryOperator

All Implemented Interfaces:

java.lang.Cloneable

Direct Known Subclasses:

ExistsOperator, InSubqueryOperator, ScalarSubquery
```
public abstract class SubqueryOperator
extends Expression
```
This class is the superclass of all expressions that can hold subqueries, such as the IN operator, the EXISTS operator, and scalar subqueries.

Subqueries are different from other kinds of expressions in that they require an execution plan to evaluate the subquery expression node. Thus, evaluating the subquery expression requires a recursive invocation of the query evaluator. In general, this recursive invocation approach will be slow for larger queries, and a good planner/optimizer will replace subquery operators with joins, semijoins, etc. wherever it can.

Note that all subqueries are considered "black boxes" to the expression-traversal mechanism. That is, traversing an expression that contains a subquery will not descend into the subquery's expressions. The reason for this is simple - the subquery may include column-references to schemas that only make sense in the context of the subquery; thus, the subquery should be processed separately from the expression traversal.

See Also:

SubquerySchemaComputer

Field Summary

Fields
Modifier and Type	Field	Description
`protected SelectClause`	`subquery`	This is the parsed representation of the subquery that the operator uses for its operation.
`protected PlanNode`	`subqueryPlan`	The execution plan for the subquery that is used by the operator.

Constructor Summary

Constructors
Constructor Description

SubqueryOperator()

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`SelectClause`	`getSubquery()`	Returns the parsed representation of the subquery that is used by this operator.
`PlanNode`	`getSubqueryPlan()`	Retrieves the current execution plan for the subquery.
`void`	`setSubqueryPlan(PlanNode plan)`	Sets the execution plan for evaluating the subquery.

Methods inherited from class edu.caltech.nanodb.expressions.Expression
clone, duplicate, equals, evaluate, evaluate, evaluatePredicate, evaluatePredicate, getAllSymbols, getColumnInfo, hashCode, hasSymbols, simplify, traverse

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

- Field Detail
  - subquery
```
protected SelectClause subquery
```
    This is the parsed representation of the subquery that the operator uses for its operation.
  - subqueryPlan
```
protected PlanNode subqueryPlan
```
    The execution plan for the subquery that is used by the operator. This will be null until the subquery has actually been analyzed and planned by the query planner.
- Constructor Detail
  - SubqueryOperator
```
public SubqueryOperator()
```
- Method Detail
  - getSubquery
```
public SelectClause getSubquery()
```
    Returns the parsed representation of the subquery that is used by this operator.
    
    Returns:
    
    the parsed representation of the subquery that is used by this operator.
  - setSubqueryPlan
```
public void setSubqueryPlan(PlanNode plan)
```
    Sets the execution plan for evaluating the subquery.
    
    Parameters:
    
    plan - the execution plan for evaluating the subquery.
  - getSubqueryPlan
```
public PlanNode getSubqueryPlan()
```
    Retrieves the current execution plan for the subquery.
    
    Returns:
    
    the current execution plan for the subquery.