org.h2.expression
Class Comparison

java.lang.Object
  extended by org.h2.expression.Expression
      extended by org.h2.expression.Condition
          extended by org.h2.expression.Comparison

public class Comparison
extends Condition

Example comparison expressions are ID=1, NAME=NAME, NAME IS NULL.


Field Summary
static int BIGGER
          The comparison type meaning > as in ID>1.
static int BIGGER_EQUAL
          The comparison type meaning >= as in ID>=1.
static int EQUAL
          The comparison type meaning = as in ID=1.
static int FALSE
          This is a pseudo comparison type that is only used for index conditions.
static int IN_LIST
          This is a pseudo comparison type that is only used for index conditions.
static int IN_QUERY
          This is a pseudo comparison type that is only used for index conditions.
static int IS_NOT_NULL
          The comparison type meaning IS NOT NULL as in NAME IS NOT NULL.
static int IS_NULL
          The comparison type meaning IS NULL as in NAME IS NULL.
static int NOT_EQUAL
          The comparison type meaning <> as in ID<>1.
static int SMALLER
          The comparison type meaning < as in ID<1.
static int SMALLER_EQUAL
          The comparison type meaning <= as in ID<=1.
 
Constructor Summary
Comparison(Session session, int compareType, Expression left, Expression right)
           
 
Method Summary
 void addFilterConditions(TableFilter filter, boolean outerJoin)
          Add conditions to a table filter if they can be evaluated.
 void createIndexConditions(Session session, TableFilter filter)
          Create index conditions if possible and attach them to the table filter.
 int getCost()
          Estimate the cost to process the expression.
 Expression getExpression(boolean getLeft)
          Get the left or the right sub-expression of this condition.
 Expression getNotIfPossible(Session session)
          If it is possible, return the negated expression.
 java.lang.String getSQL()
          Get the SQL statement of this expression.
 Value getValue(Session session)
          Return the resulting value for the current row.
 boolean isEverything(ExpressionVisitor visitor)
          Check if this expression and all sub-expressions can fulfill a criteria.
 void mapColumns(ColumnResolver resolver, int level)
          Map the columns of the resolver to expression columns.
 Expression optimize(Session session)
          Try to optimize the expression.
 void setEvaluatable(TableFilter tableFilter, boolean b)
          Tell the expression columns whether the table filter can return values now.
 void updateAggregate(Session session)
          Update an aggregate value.
 
Methods inherited from class org.h2.expression.Condition
getDisplaySize, getPrecision, getScale, getType
 
Methods inherited from class org.h2.expression.Expression
getAlias, getBooleanValue, getColumnName, getNonAliasExpression, getNullable, getSchemaName, getTableAlias, getTableName, isAutoIncrement, isConstant, isEverything, isValueSet, isWildcard, optimizeInJoin, toString
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

EQUAL

public static final int EQUAL
The comparison type meaning = as in ID=1.

See Also:
Constant Field Values

BIGGER_EQUAL

public static final int BIGGER_EQUAL
The comparison type meaning >= as in ID>=1.

See Also:
Constant Field Values

BIGGER

public static final int BIGGER
The comparison type meaning > as in ID>1.

See Also:
Constant Field Values

SMALLER_EQUAL

public static final int SMALLER_EQUAL
The comparison type meaning <= as in ID<=1.

See Also:
Constant Field Values

SMALLER

public static final int SMALLER
The comparison type meaning < as in ID<1.

See Also:
Constant Field Values

NOT_EQUAL

public static final int NOT_EQUAL
The comparison type meaning <> as in ID<>1.

See Also:
Constant Field Values

IS_NULL

public static final int IS_NULL
The comparison type meaning IS NULL as in NAME IS NULL.

See Also:
Constant Field Values

IS_NOT_NULL

public static final int IS_NOT_NULL
The comparison type meaning IS NOT NULL as in NAME IS NOT NULL.

See Also:
Constant Field Values

FALSE

public static final int FALSE
This is a pseudo comparison type that is only used for index conditions. It means the comparison will always yield FALSE. Example: 1=0.

See Also:
Constant Field Values

IN_LIST

public static final int IN_LIST
This is a pseudo comparison type that is only used for index conditions. It means equals any value of a list. Example: IN(1, 2, 3).

See Also:
Constant Field Values

IN_QUERY

public static final int IN_QUERY
This is a pseudo comparison type that is only used for index conditions. It means equals any value of a list. Example: IN(SELECT ...).

See Also:
Constant Field Values
Constructor Detail

Comparison

public Comparison(Session session,
                  int compareType,
                  Expression left,
                  Expression right)
Method Detail

getSQL

public java.lang.String getSQL()
Description copied from class: Expression
Get the SQL statement of this expression. This may not always be the original SQL statement, specially after optimization.

Specified by:
getSQL in class Expression
Returns:
the SQL statement

optimize

public Expression optimize(Session session)
                    throws java.sql.SQLException
Description copied from class: Expression
Try to optimize the expression.

Specified by:
optimize in class Expression
Parameters:
session - the session
Returns:
the optimized expression
Throws:
java.sql.SQLException

getValue

public Value getValue(Session session)
               throws java.sql.SQLException
Description copied from class: Expression
Return the resulting value for the current row.

Specified by:
getValue in class Expression
Parameters:
session - the session
Returns:
the result
Throws:
java.sql.SQLException

getNotIfPossible

public Expression getNotIfPossible(Session session)
Description copied from class: Expression
If it is possible, return the negated expression. This is used to optimize NOT expressions: NOT ID>10 can be converted to ID<=10. Returns null if negating is not possible.

Overrides:
getNotIfPossible in class Expression
Parameters:
session - the session
Returns:
the negated expression, or null

createIndexConditions

public void createIndexConditions(Session session,
                                  TableFilter filter)
Description copied from class: Expression
Create index conditions if possible and attach them to the table filter.

Overrides:
createIndexConditions in class Expression
Parameters:
session - the session
filter - the table filter

setEvaluatable

public void setEvaluatable(TableFilter tableFilter,
                           boolean b)
Description copied from class: Expression
Tell the expression columns whether the table filter can return values now. This is used when optimizing the query.

Specified by:
setEvaluatable in class Expression
Parameters:
tableFilter - the table filter
b - true if the table filter can return value

updateAggregate

public void updateAggregate(Session session)
                     throws java.sql.SQLException
Description copied from class: Expression
Update an aggregate value. This method is called at statement execution time. It is usually called once for each row, but if the expression is used multiple times (for example in the column list, and as part of the HAVING expression) it is called multiple times - the row counter needs to be used to make sure the internal state is only updated once.

Specified by:
updateAggregate in class Expression
Parameters:
session - the session
Throws:
java.sql.SQLException

addFilterConditions

public void addFilterConditions(TableFilter filter,
                                boolean outerJoin)
Description copied from class: Expression
Add conditions to a table filter if they can be evaluated.

Overrides:
addFilterConditions in class Expression
Parameters:
filter - the table filter
outerJoin - if the expression is part of an outer join

mapColumns

public void mapColumns(ColumnResolver resolver,
                       int level)
                throws java.sql.SQLException
Description copied from class: Expression
Map the columns of the resolver to expression columns.

Specified by:
mapColumns in class Expression
Parameters:
resolver - the column resolver
level - the subquery nesting level
Throws:
java.sql.SQLException

isEverything

public boolean isEverything(ExpressionVisitor visitor)
Description copied from class: Expression
Check if this expression and all sub-expressions can fulfill a criteria. If any part returns false, the result is false.

Specified by:
isEverything in class Expression
Parameters:
visitor - the visitor
Returns:
if the criteria can be fulfilled

getCost

public int getCost()
Description copied from class: Expression
Estimate the cost to process the expression. Used when optimizing the query, to calculate the query plan with the lowest estimated cost.

Specified by:
getCost in class Expression
Returns:
the estimated cost

getExpression

public Expression getExpression(boolean getLeft)
Get the left or the right sub-expression of this condition.

Parameters:
getLeft - true to get the left sub-expression, false to get the right sub-expression.
Returns:
the sub-expression