Class ExistsOperator
- java.lang.Object
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- edu.caltech.nanodb.expressions.Expression
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- edu.caltech.nanodb.expressions.SubqueryOperator
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- edu.caltech.nanodb.expressions.ExistsOperator
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- All Implemented Interfaces:
java.lang.Cloneable
public class ExistsOperator extends SubqueryOperator
This class implements the EXISTS (subquery) operator. This operation may be optimized out of a query, but if it is not, it can still be evaluated although it will be slow.
The NOT EXISTS (subquery) clause is translated into NOT (EXISTS (subquery)) by the parser, as expected.
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Field Summary
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Fields inherited from class edu.caltech.nanodb.expressions.SubqueryOperator
subquery, subqueryPlan
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Constructor Summary
Constructors Constructor Description ExistsOperator(SelectClause subquery)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description protected java.lang.Object
clone()
Creates a copy of expression.boolean
equals(java.lang.Object obj)
Checks if the argument is an expression with the same structure, but not necessarily the same references.java.lang.Object
evaluate(Environment env)
Evaluates this expression object in the context of the specified environment.ColumnInfo
getColumnInfo(Schema schema)
Returns aColumnInfo
object describing the type (and possibly the name) of the expression's result.int
hashCode()
Computes the hashcode of an Expression.java.lang.String
toString()
Returns a string representation of this EXISTS expression.Expression
traverse(ExpressionProcessor p)
This method allows the entire expression tree to be traversed node by node, either for analysis or for transformation.-
Methods inherited from class edu.caltech.nanodb.expressions.SubqueryOperator
getSubquery, getSubqueryPlan, setSubqueryPlan
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Methods inherited from class edu.caltech.nanodb.expressions.Expression
duplicate, evaluate, evaluatePredicate, evaluatePredicate, getAllSymbols, hasSymbols, simplify
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Constructor Detail
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ExistsOperator
public ExistsOperator(SelectClause subquery)
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Method Detail
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getColumnInfo
public ColumnInfo getColumnInfo(Schema schema) throws SchemaNameException
Description copied from class:Expression
Returns aColumnInfo
object describing the type (and possibly the name) of the expression's result.- Specified by:
getColumnInfo
in classExpression
- Parameters:
schema
- a schema object that can be used to look up name and type details for symbols referenced by the expression.- Returns:
- a column-information object describing the type (and possibly the name and table-name) of this expression's result
- Throws:
SchemaNameException
- if a symbol cannot be resolved, either because it doesn't appear in the schema, or because the name is ambiguous.
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evaluate
public java.lang.Object evaluate(Environment env) throws ExpressionException
Description copied from class:Expression
Evaluates this expression object in the context of the specified environment. The environment provides any external information necessary to evaluate the expression, such as the current tuples loaded from tables referenced within the expression.- Specified by:
evaluate
in classExpression
- Parameters:
env
- the environment to look up symbol-values from, when evaluating the expression- Returns:
- the result of the expression evaluation
- Throws:
ExpressionException
- if the expression cannot be evaluated for some reason.
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traverse
public Expression traverse(ExpressionProcessor p)
Description copied from class:Expression
This method allows the entire expression tree to be traversed node by node, either for analysis or for transformation. The
ExpressionProcessor
instance receives notifications as each node in the expression is entered and left.The expression tree can also be manipulated by this traversal process, depending on what the
ExpressionProcessor
wants to do. If the expression node thattraverse()
is invoked on, needs to be replaced with a new expression node, the replacement is returned by thetraverse()
method. (TheExpressionProcessor
specifies the replacement as the return-value from theExpressionProcessor.leave(Expression)
method.)- Specified by:
traverse
in classExpression
- Parameters:
p
- the object that performs analysis or transformation of the expression tree- Returns:
- an
Expression
node to replace this node, ornull
if no changes are to be made.
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toString
public java.lang.String toString()
Returns a string representation of this EXISTS expression.- Overrides:
toString
in classjava.lang.Object
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equals
public boolean equals(java.lang.Object obj)
Checks if the argument is an expression with the same structure, but not necessarily the same references.- Specified by:
equals
in classExpression
- Parameters:
obj
- the object to which we are comparing
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hashCode
public int hashCode()
Description copied from class:Expression
Computes the hashcode of an Expression. This method is used to see if two expressions CAN be equal.- Specified by:
hashCode
in classExpression
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clone
protected java.lang.Object clone() throws java.lang.CloneNotSupportedException
Creates a copy of expression. This method is used by theExpression.duplicate()
method to make a deep copy of an expression tree.- Overrides:
clone
in classExpression
- Throws:
java.lang.CloneNotSupportedException
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