SubquerySchemaComputer (NanoDB SQL Relational Database 0.1-SNAPSHOT API)

java.lang.Object
- edu.caltech.nanodb.queryast.SubquerySchemaComputer

All Implemented Interfaces:

ExpressionProcessor
```
class SubquerySchemaComputer
extends java.lang.Object
implements ExpressionProcessor
```
This expression-processor implementation looks for subqueries within an expression, and calls the SelectClause.computeSchema(edu.caltech.nanodb.storage.TableManager, edu.caltech.nanodb.queryast.SelectClause) method on them. The enclosing query is passed as an argument, in case subqueries are correlated with the enclosing query.

Note that this traversal mechanism will only identify the subqueries that are immediately nested within this query; if a subquery itself has subqueries, those will not be identified by this class, but rather will be processed when the subquery's schema is computed.

Field Summary

Fields
Modifier and Type	Field	Description
`private boolean`	`found`	A flag used to track whether subqueries were found while traversing the expression tree.
`private static org.apache.logging.log4j.Logger`	`logger`	A logging object for reporting anything interesting that happens.
`private SelectClause`	`selectClause`	This is the parent query that may contain subqueries.
`private TableManager`	`tableManager`	This is the table-manager used to access table schemas.

Constructor Summary

Constructors
Constructor Description

SubquerySchemaComputer(SelectClause selectClause, TableManager tableManager)

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`clearFoundFlag()`
`void`	`enter(Expression e)`	This method identifies `SubqueryOperator` objects, retrieves the subquery, and then generates a plan for the subquery.
`boolean`	`foundSubqueries()`
`Expression`	`leave(Expression e)`	This method is a no-op for this expression processor.

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

- Field Detail
  - logger
```
private static org.apache.logging.log4j.Logger logger
```
    A logging object for reporting anything interesting that happens.
  - selectClause
```
private SelectClause selectClause
```
    This is the parent query that may contain subqueries.
  - tableManager
```
private TableManager tableManager
```
    This is the table-manager used to access table schemas.
  - found
```
private boolean found
```
    A flag used to track whether subqueries were found while traversing the expression tree.
- Constructor Detail
  - SubquerySchemaComputer
```
public SubquerySchemaComputer(SelectClause selectClause,
                              TableManager tableManager)
```
- Method Detail
  - enter
```
public void enter(Expression e)
```
    This method identifies SubqueryOperator objects, retrieves the subquery, and then generates a plan for the subquery.
    
    Specified by:
    
    enter in interface ExpressionProcessor
    
    Parameters:
    
    e - the expression node being entered
  - leave
```
public Expression leave(Expression e)
```
    This method is a no-op for this expression processor.
    
    Specified by:
    
    leave in interface ExpressionProcessor
    
    Parameters:
    
    e - the expression node being left
    
    Returns:
    
    the passed-in expression e.
  - foundSubqueries
```
public boolean foundSubqueries()
```
  - clearFoundFlag
```
public void clearFoundFlag()
```