Package org.h2.expression

Class Subquery

  • All Implemented Interfaces:
    HasSQL, Typed
    public final class Subquery
extends Expression
    A query returning a single value. Subqueries are used inside other statements.

    • Field Detail

      • query

        private final Query query

      • nullValue

        private Value nullValue

      • outerResolvers

        private java.util.HashSet<ColumnResolver> outerResolvers

    • Constructor Detail

      • Subquery

        public Subquery​(Query query)

    • Method Detail

      • getValue

        public Value getValue​(SessionLocal session)
        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

      • getAllRows

        public java.util.ArrayList<Value> getAllRows​(SessionLocal session)
        Evaluates and returns all rows of the subquery.
        Parameters:
        session - the session
        Returns:
        values in all rows

      • getType

        public TypeInfo getType()
        Description copied from class: Expression
        Returns the data type. The data type may be unknown before the optimization phase.
        Specified by:
        getType in interface Typed
        Specified by:
        getType in class Expression
        Returns:
        the data type

      • mapColumns

        public void mapColumns​(ColumnResolver resolver,
                       int level,
                       int state)
        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
        state - current state for nesting checks, initial value is Expression.MAP_INITIAL

      • optimize

        public Expression optimize​(SessionLocal session)
        Description copied from class: Expression
        Try to optimize the expression.
        Specified by:
        optimize in class Expression
        Parameters:
        session - the session
        Returns:
        the optimized expression

      • setType

        private void setType()

      • 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

      • getUnenclosedSQL

        public java.lang.StringBuilder getUnenclosedSQL​(java.lang.StringBuilder builder,
                                                int sqlFlags)
        Description copied from class: Expression
        Get the SQL statement of this expression. This may not always be the original SQL statement, especially after optimization. Enclosing '(' and ')' are never appended.
        Specified by:
        getUnenclosedSQL in class Expression
        Parameters:
        builder - string builder
        sqlFlags - formatting flags
        Returns:
        the specified string builder

      • updateAggregate

        public void updateAggregate​(SessionLocal session,
                            int stage)
        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
        stage - select stage

      • 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

      • getQuery

        public Query getQuery()

      • 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

      • isConstant

        public boolean isConstant()
        Description copied from class: Expression
        Check if this expression will always return the same value.
        Overrides:
        isConstant in class Expression
        Returns:
        if the expression is constant