Class SubqueryNode

All Implemented Interfaces:
Visitable

class SubqueryNode extends ValueNode
A SubqueryNode represents a subquery. Subqueries return values to their outer queries. An quantified subquery is one that appears under a quantified operator (like IN or EXISTS) - quantified subqueries can return more than one value per invocation. An expression subquery is one that is not directly under a quantified operator - expression subqueries are allowed to return at most one value per invocation (returning no value is considered to be equivalent to returning NULL). There are a large number of subquery types. Because of the large number of types, and the large amount of shared code, we have decided to have 1 SubqueryNode without any subclasses. The subquery type (and operator) is encoded in the subqueryType field. The query optimizer is responsible for optimizing subqueries, and also for transforming them so that code can be generated for them. The optimizer may eliminate some subqueries by transforming them into joins, or it may change the internal form of a subquery (for example, transforming 'where x in (select y from z where ...)' into 'where (select true from z where x = y and ...)'). Note that aggregates present some additional issues. A transformation such as:
    where x in (SELECT expression FROM z)
has to be treated specially if expression has an aggregate. We change it to:
    where x = (SELECT true FROM (SELECT MAX(x) FROM z) WHERE SQLCOL1 = y)
  • Field Details

    • resultSet

      ResultSetNode resultSet
    • subqueryType

      int subqueryType
    • underTopAndNode

      boolean underTopAndNode
    • preprocessed

      boolean preprocessed
    • distinctExpression

      boolean distinctExpression
    • whereSubquery

      boolean whereSubquery
    • leftOperand

      ValueNode leftOperand
    • pushedNewPredicate

      boolean pushedNewPredicate
    • havingSubquery

      boolean havingSubquery
      is this subquery part of a having clause. We need to know this so we can avoid flattening.
    • parentComparisonOperator

      BinaryComparisonOperatorNode parentComparisonOperator
    • trueNode

      private BooleanConstantNode trueNode
    • subqueryNumber

      private int subqueryNumber
    • pointOfAttachment

      private int pointOfAttachment
    • foundCorrelation

      private boolean foundCorrelation
    • doneCorrelationCheck

      private boolean doneCorrelationCheck
    • foundVariant

      private boolean foundVariant
    • doneInvariantCheck

      private boolean doneInvariantCheck
    • orderByList

      private OrderByList orderByList
    • offset

      private ValueNode offset
    • fetchFirst

      private ValueNode fetchFirst
    • hasJDBClimitClause

      private boolean hasJDBClimitClause
    • NOTIMPLEMENTED_SUBQUERY

      static final int NOTIMPLEMENTED_SUBQUERY
      See Also:
    • FROM_SUBQUERY

      static final int FROM_SUBQUERY
      See Also:
    • IN_SUBQUERY

      static final int IN_SUBQUERY
      See Also:
    • NOT_IN_SUBQUERY

      static final int NOT_IN_SUBQUERY
      See Also:
    • EQ_ANY_SUBQUERY

      static final int EQ_ANY_SUBQUERY
      See Also:
    • EQ_ALL_SUBQUERY

      static final int EQ_ALL_SUBQUERY
      See Also:
    • NE_ANY_SUBQUERY

      static final int NE_ANY_SUBQUERY
      See Also:
    • NE_ALL_SUBQUERY

      static final int NE_ALL_SUBQUERY
      See Also:
    • GT_ANY_SUBQUERY

      static final int GT_ANY_SUBQUERY
      See Also:
    • GT_ALL_SUBQUERY

      static final int GT_ALL_SUBQUERY
      See Also:
    • GE_ANY_SUBQUERY

      static final int GE_ANY_SUBQUERY
      See Also:
    • GE_ALL_SUBQUERY

      static final int GE_ALL_SUBQUERY
      See Also:
    • LT_ANY_SUBQUERY

      static final int LT_ANY_SUBQUERY
      See Also:
    • LT_ALL_SUBQUERY

      static final int LT_ALL_SUBQUERY
      See Also:
    • LE_ANY_SUBQUERY

      static final int LE_ANY_SUBQUERY
      See Also:
    • LE_ALL_SUBQUERY

      static final int LE_ALL_SUBQUERY
      See Also:
    • EXISTS_SUBQUERY

      static final int EXISTS_SUBQUERY
      See Also:
    • NOT_EXISTS_SUBQUERY

      static final int NOT_EXISTS_SUBQUERY
      See Also:
    • EXPRESSION_SUBQUERY

      static final int EXPRESSION_SUBQUERY
      See Also:
  • Constructor Details

    • SubqueryNode

      SubqueryNode(ResultSetNode resultSet, int subqueryType, ValueNode leftOperand, OrderByList orderCols, ValueNode offset, ValueNode fetchFirst, boolean hasJDBClimitClause, ContextManager cm)
      Constructor.
      Parameters:
      resultSet - The ResultSetNode for the subquery
      subqueryType - The type of the subquery
      leftOperand - The left operand, if any, of the subquery
      orderCols - ORDER BY list
      offset - OFFSET n ROWS
      fetchFirst - FETCH FIRST n ROWS ONLY
      hasJDBClimitClause - True if the offset/fetchFirst clauses come from JDBC limit/offset escape syntax
      cm - Context Manager
  • Method Details

    • toString

      public String toString()
      Convert this object to a String. See comments in QueryTreeNode.java for how this should be done for tree printing.
      Overrides:
      toString in class ValueNode
      Returns:
      This object as a String
    • printSubNodes

      void printSubNodes(int depth)
      Prints the sub-nodes of this object. See QueryTreeNode.java for how tree printing is supposed to work.
      Overrides:
      printSubNodes in class QueryTreeNode
      Parameters:
      depth - The depth of this node in the tree
    • getResultSet

      ResultSetNode getResultSet()
      Return the resultSet for this SubqueryNode.
      Returns:
      ResultSetNode underlying this SubqueryNode.
    • getSubqueryType

      int getSubqueryType()
      Return the type of this subquery.
      Returns:
      int Type of this subquery.
    • setSubqueryType

      void setSubqueryType(int subqueryType)
      Set the type of this subquery.
      Parameters:
      subqueryType - of this subquery.
    • setPointOfAttachment

      void setPointOfAttachment(int pointOfAttachment) throws StandardException
      Set the point of attachment of this subquery.
      Parameters:
      pointOfAttachment - The point of attachment of this subquery.
      Throws:
      StandardException - Thrown on error
    • getUnderTopAndNode

      boolean getUnderTopAndNode()
      Return whether or not this subquery is immediately under a top level AndNode.
      Returns:
      boolean Whether or not this subquery is immediately under a top level AndNode.
    • getPointOfAttachment

      int getPointOfAttachment()
      Get the ResultSet # for the point of attachment for this SubqueryNode.
      Returns:
      int The ResultSet # for the point of attachment
    • getPreprocessed

      boolean getPreprocessed()
      Get whether or not this SubqueryNode has already been preprocessed.
      Returns:
      Whether or not this SubqueryNode has already been preprocessed.
    • setParentComparisonOperator

      void setParentComparisonOperator(BinaryComparisonOperatorNode parent)
      Set the parent BCON. Useful when considering flattening expression subqueries.
      Parameters:
      parent - The parent BCON.
    • referencesSessionSchema

      public boolean referencesSessionSchema() throws StandardException
      Description copied from class: QueryTreeNode
      Return true if the node references SESSION schema tables (temporary or permanent)
      Overrides:
      referencesSessionSchema in class QueryTreeNode
      Returns:
      true if references SESSION schema tables, else false
      Throws:
      StandardException - Thrown on error
    • remapColumnReferencesToExpressions

      ValueNode remapColumnReferencesToExpressions() throws StandardException
      Remap all ColumnReferences in this tree to be clones of the underlying expression.
      Overrides:
      remapColumnReferencesToExpressions in class ValueNode
      Returns:
      ValueNode The remapped expression tree.
      Throws:
      StandardException - Thrown on error
    • bindExpression

      ValueNode bindExpression(FromList fromList, SubqueryList subqueryList, List<AggregateNode> aggregates) throws StandardException
      Bind this expression. This means binding the sub-expressions, as well as figuring out what the return type is for this expression.
      Overrides:
      bindExpression in class ValueNode
      Parameters:
      fromList - The FROM list for the query this expression is in, for binding columns. NOTE: fromList will be null if the subquery appears in a VALUES clause.
      subqueryList - The subquery list being built as we find SubqueryNodes
      aggregates - The aggregate list being built as we find AggregateNodes
      Returns:
      The new top of the expression tree.
      Throws:
      StandardException - Thrown on error
    • preprocess

      ValueNode preprocess(int numTables, FromList outerFromList, SubqueryList outerSubqueryList, PredicateList outerPredicateList) throws StandardException
      Preprocess an expression tree. We do a number of transformations here (including subqueries, IN lists, LIKE and BETWEEN) plus subquery flattening. NOTE: This is done before the outer ResultSetNode is preprocessed.
      Overrides:
      preprocess in class ValueNode
      Parameters:
      numTables - Number of tables in the DML Statement
      outerFromList - FromList from outer query block
      outerSubqueryList - SubqueryList from outer query block
      outerPredicateList - PredicateList from outer query block
      Returns:
      The modified expression
      Throws:
      StandardException - Thrown on error
    • singleFromBaseTable

      private FromBaseTable singleFromBaseTable(FromList fromList)
      Does the from list from the subquery contain a single entry which is a FBT or a PRN/FBT.
      Parameters:
      fromList - The from list from the subquery
      Returns:
      the FromBaseTable if the from list from the subquery contains a single entry which is a FBT or a PRN/FBT, or null if the subquery does not contain a single FBT
    • rightOperandFlattenableToNotExists

      private boolean rightOperandFlattenableToNotExists(int numTables, FromBaseTable fbt) throws StandardException

      Check if the right operand is on a form that makes it possible to flatten this query to a NOT EXISTS join. We don't allow flattening if the right operand doesn't reference the base table of the subquery. (Requirement added as part of DERBY-4001.)

      The problem with the right operand not referencing the base table of the subquery, is that the join condition may then be used to filter rows from the right side (outer) table in the NOT EXISTS join. In a NOT EXISTS join, the join condition can only safely be applied to the left side (inner) table of the join. Otherwise, it will filter out all the interesting rows too early.

      Take the query below as an example:

      
       SELECT * FROM T1 WHERE X NOT IN (SELECT 1 FROM T2)
       

      Here, the right operand is 1, and the join condition is T1.X=1. If flattened, the join condition will be used directly on the outer table, and hide all rows with X<>1, although those are the only rows we're interested in. If the join condition had only been used on the inner table, the NOT EXISTS join logic would do the correct thing.

      If the join condition references the inner table, the condition cannot be used directly on the outer table, so it is safe to flatten the query.

      Parameters:
      numTables - the number of tables in this statement
      fbt - the only FromBaseTable in this subquery
      Returns:
      true if it is OK to flatten this query to a NOT EXISTS join, false otherwise
      Throws:
      StandardException
    • canAllBeFlattened

      private boolean canAllBeFlattened() throws StandardException
      Can NOT IN, ALL be falttened to NOT EXISTS join? We can't or the flattening doesn't easily make sense if either side of the comparison is nullable. (beetle 5173)
      Returns:
      Whether or not the NOT IN or ALL subquery can be flattened.
      Throws:
      StandardException
    • flattenToNormalJoin

      private ValueNode flattenToNormalJoin(int numTables, FromList outerFromList, SubqueryList outerSubqueryList, PredicateList outerPredicateList) throws StandardException
      Flatten this subquery into the outer query block. At this point we are only flattening based on a uniqueness condition and only flattening non-aggregate subqueries. So, we promote the subquery's from list, as is, into the outer from list. For EXISTS subquerys, we return a TRUE. Otherwise we return a new comparison between the leftOperand and the expression in the subquery's SELECT list. RESOLVE - we will need to modify this logic to account for exists joins and aggregates as we support flattening for them. Anyway, here's what we do: o We remove ourself from the outer subquery list. o We decrement the nesting level for all tables in the subquery tree. o We append the subquery's from list to the outer from list. o We add the subquery's predicate list to the outer predicate list. (The subquery has already been preprocessed.) o We add the subquery's subquery list to the outer subquery list. o For EXISTS, we return a true. o Otherwise, we return a new comparison between the leftOperand and the expression in the inner select's RCL.
      Parameters:
      numTables - Number of tables in the DML Statement
      outerFromList - FromList from outer query block
      outerSubqueryList - SubqueryList from outer query block
      outerPredicateList - PredicateList from outer query block
      Returns:
      The modified expression
      Throws:
      StandardException - Thrown on error
    • flattenToExistsJoin

      private ValueNode flattenToExistsJoin(int numTables, FromList outerFromList, SubqueryList outerSubqueryList, PredicateList outerPredicateList, boolean flattenableNotExists) throws StandardException
      Flatten this subquery into the outer query block as an exists join. At this point we are only flattening non-aggregate subqueries with a single FBT in the from list. So, we transform all FBTs in the from list into ExistBaseTables, update the dependency lists for each of the tables and then flatten the subquery. RESOLVE - we will need to modify this logic to account for aggregates as we support flattening for them.
      Parameters:
      numTables - Number of tables in the DML Statement
      outerFromList - FromList from outer query block
      outerSubqueryList - SubqueryList from outer query block
      outerPredicateList - PredicateList from outer query block
      flattenableNotExists - Is it a flattening into a NOT EXISTS join
      Returns:
      The modified expression
      Throws:
      StandardException - Thrown on error
    • getRightOperand

      private ValueNode getRightOperand()
      Get the node that will be the right operand in the join condition if this ALL/ANY/SOME/(NOT) IN subquery is flattened to a join.
      Returns:
      the right operand
    • isInvariant

      private boolean isInvariant() throws StandardException
      Check to see if we have a Variant value below us. If so, return true. Caches the result so multiple calls are ok.
      Returns:
      boolean whether we have
      Throws:
      StandardException - Thrown on error
    • hasCorrelatedCRs

      boolean hasCorrelatedCRs() throws StandardException
      Check to see if this subquery has correlated column references. Only useful results if called AFTER binding (after CRs have been bound).
      Returns:
      whether the subquery has correlated column references.
      Throws:
      StandardException - Thrown on error
    • pushNewPredicate

      private UnaryComparisonOperatorNode pushNewPredicate(int numTables) throws StandardException
      Transform: expression QuantifiedOperator (select x from ...) into (select true from .. where expression x ...) IS [NOT] NULL or, if we have an aggregate: (select true from (select AGG(x) from ...) where expression x ...) IS [NOT] NULL For ANY and IN subqueries: o We generate an IS NULL above the SubqueryNode and return the top of the new tree to the caller. o The operator in the new predicate that is added to the subquery will correspond to the operator that modifies the ANY. (eg, = for = ANY, with = for IN.) For ALL and NOT IN subqueries: o We generate an IS NOT NULL above the SubqueryNode and return the top of the new tree to the caller. o The operator in the new predicate that is added to the subquery will be a BinaryAllOperatorNode whose bcoNodeType corresponds to the negation of the operator that modifies the ALL. (eg, <> for = ALL, with <> for NOT IN.) NOTE: This method is called after the underlying subquery has been preprocessed, so we build a new Predicate, not just a new expression.
      Parameters:
      numTables - Number of tables in DML Statement
      Returns:
      UnaryComparisonOperatorNode An IS [NOT] NULL above the transformed subquery.
      Throws:
      StandardException - Thrown on error
    • getNewJoinCondition

      private BinaryComparisonOperatorNode getNewJoinCondition(ValueNode leftOperand, ValueNode rightOperand) throws StandardException
      Build a new join condition between the leftOperand and the rightOperand. The comparison operator is dependent on the subquery type.
      Parameters:
      leftOperand - The left operand for the new condition.
      rightOperand - The right operand for the new condition.
      Throws:
      StandardException - Thrown on error
    • eliminateNots

      ValueNode eliminateNots(boolean underNotNode) throws StandardException
      Eliminate NotNodes in the current query block. We traverse the tree, inverting ANDs and ORs and eliminating NOTs as we go. We stop at ComparisonOperators and boolean expressions. We invert ComparisonOperators and replace boolean expressions with boolean expression = false. NOTE: Since we do not recurse under ComparisonOperators, there still could be NotNodes left in the tree.
      Overrides:
      eliminateNots in class ValueNode
      Parameters:
      underNotNode - Whether or not we are under a NotNode.
      Returns:
      The modified expression
      Throws:
      StandardException - Thrown on error
    • changeToCNF

      ValueNode changeToCNF(boolean underTopAndNode) throws StandardException
      Finish putting an expression into conjunctive normal form. An expression tree in conjunctive normal form meets the following criteria: o If the expression tree is not null, the top level will be a chain of AndNodes terminating in a true BooleanConstantNode. o The left child of an AndNode will never be an AndNode. o Any right-linked chain that includes an AndNode will be entirely composed of AndNodes terminated by a true BooleanConstantNode. o The left child of an OrNode will never be an OrNode. o Any right-linked chain that includes an OrNode will be entirely composed of OrNodes terminated by a false BooleanConstantNode. o ValueNodes other than AndNodes and OrNodes are considered leaf nodes for purposes of expression normalization. In other words, we won't do any normalization under those nodes. In addition, we track whether or not we are under a top level AndNode. SubqueryNodes need to know this for subquery flattening.
      Overrides:
      changeToCNF in class ValueNode
      Parameters:
      underTopAndNode - Whether or not we are under a top level AndNode.
      Returns:
      The modified expression
      Throws:
      StandardException - Thrown on error
    • categorize

      boolean categorize(JBitSet referencedTabs, boolean simplePredsOnly) throws StandardException
      Categorize this predicate. Initially, this means building a bit map of the referenced tables for each predicate. If the source of this ColumnReference (at the next underlying level) is not a ColumnReference or a VirtualColumnNode then this predicate will not be pushed down. For example, in: select * from (select 1 from s) a (x) where x = 1 we will not push down x = 1. NOTE: It would be easy to handle the case of a constant, but if the inner SELECT returns an arbitrary expression, then we would have to copy that tree into the pushed predicate, and that tree could contain subqueries and method calls. RESOLVE - revisit this issue once we have views.
      Overrides:
      categorize in class ValueNode
      Parameters:
      referencedTabs - JBitSet with bit map of referenced FromTables
      simplePredsOnly - Whether or not to consider method calls, field references and conditional nodes when building bit map
      Returns:
      boolean Whether or not source.expression is a ColumnReference or a VirtualColumnNode.
      Throws:
      StandardException - Thrown on error
    • isMaterializable

      public boolean isMaterializable() throws StandardException
      Throws:
      StandardException
    • optimize

      void optimize(DataDictionary dataDictionary, double outerRows) throws StandardException
      Optimize this SubqueryNode.
      Parameters:
      dataDictionary - The DataDictionary to use for optimization
      outerRows - The optimizer's estimate of the number of times this subquery will be executed.
      Throws:
      StandardException - Thrown on error
    • modifyAccessPaths

      void modifyAccessPaths() throws StandardException
      Make any changes to the access paths, as decided by the optimizer.
      Throws:
      StandardException - Thrown on error
    • getOrderableVariantType

      protected int getOrderableVariantType() throws StandardException
      Return the variant type for the underlying expression. The variant type can be: VARIANT - variant within a scan (method calls and non-static field access) SCAN_INVARIANT - invariant within a scan (column references from outer tables) QUERY_INVARIANT - invariant within the life of a query (constant expressions)
      Overrides:
      getOrderableVariantType in class ValueNode
      Returns:
      The variant type for the underlying expression.
      Throws:
      StandardException - Thrown on error
    • generateExpression

      void generateExpression(ExpressionClassBuilder expressionBuilder, MethodBuilder mbex) throws StandardException
      Do code generation for this subquery.
      Overrides:
      generateExpression in class ValueNode
      Parameters:
      expressionBuilder - The ExpressionClassBuilder for the class being built
      mbex - The method the expression will go into
      Throws:
      StandardException - Thrown on error
    • generateMaterialization

      private LocalField generateMaterialization(ActivationClassBuilder acb, MethodBuilder mbsq, String type)
    • getTrueNode

      private BooleanConstantNode getTrueNode() throws StandardException
      Throws:
      StandardException
    • acceptChildren

      void acceptChildren(Visitor v) throws StandardException
      Accept the visitor for all visitable children of this node.
      Overrides:
      acceptChildren in class QueryTreeNode
      Parameters:
      v - the visitor
      Throws:
      StandardException - on error
    • isIN

      private boolean isIN()
    • isNOT_IN

      private boolean isNOT_IN()
    • isANY

      private boolean isANY()
    • isALL

      private boolean isALL()
    • isEXISTS

      private boolean isEXISTS()
    • isNOT_EXISTS

      private boolean isNOT_EXISTS()
    • changeToCorrespondingExpressionType

      private void changeToCorrespondingExpressionType() throws StandardException
      Convert this IN/ANY subquery, which is known to return at most 1 row, to an equivalent expression subquery.
      Throws:
      StandardException - Thrown on error
    • setDataTypeServices

      private void setDataTypeServices(ResultColumnList resultColumns) throws StandardException
      Throws:
      StandardException
    • isEquivalent

      boolean isEquivalent(ValueNode o)
      Tests if this node is equivalent to the specified ValueNode. Two ValueNodes are considered equivalent if they will evaluate to the same value during query execution.

      This method provides basic expression matching facility for the derived class of ValueNode and it is used by the language layer to compare the node structural form of the two expressions for equivalence at bind phase.

      Note that it is not comparing the actual row values at runtime to produce a result; hence, when comparing SQL NULLs, they are considered to be equivalent and not unknown.

      One usage case of this method in this context is to compare the select column expression against the group by expression to check if they are equivalent. e.g.:

      SELECT c1+c2 FROM t1 GROUP BY c1+c2

      In general, node equivalence is determined by the derived class of ValueNode. But they generally abide to the rules below:

      • The two ValueNodes must be of the same node type to be considered equivalent. e.g.: CastNode vs. CastNode - equivalent (if their args also match), ColumnReference vs CastNode - not equivalent.
      • If node P contains other ValueNode(s) and so on, those node(s) must also be of the same node type to be considered equivalent.
      • If node P takes a parameter list, then the number of arguments and its arguments for the two nodes must also match to be considered equivalent. e.g.: CAST(c1 as INTEGER) vs CAST(c1 as SMALLINT), they are not equivalent.
      • When comparing SQL NULLs in this context, they are considered to be equivalent.
      • If this does not apply or it is determined that the two nodes are not equivalent then the derived class of this method should return false; otherwise, return true.
      Specified by:
      isEquivalent in class ValueNode
      Parameters:
      o - the node to compare this ValueNode against.
      Returns:
      true if the two nodes are equivalent, false otherwise.
    • isHavingSubquery

      public boolean isHavingSubquery()
      Is this subquery part of a having clause?
      Returns:
      true if it is part of a having clause, otherwise false
    • setHavingSubquery

      public void setHavingSubquery(boolean havingSubquery)
      Mark this subquery as being part of a having clause.
      Parameters:
      havingSubquery -
    • isWhereSubquery

      boolean isWhereSubquery()
      Is this subquery part of a whereclause?
      Returns:
      true if it is part of a where clause, otherwise false
    • setWhereSubquery

      void setWhereSubquery(boolean whereSubquery)
      Mark this subquery as being part of a where clause.
      Parameters:
      whereSubquery -
    • isWhereExistsAnyInWithWhereSubquery

      boolean isWhereExistsAnyInWithWhereSubquery() throws StandardException
      Check whether this is a WHERE EXISTS | ANY | IN subquery with a subquery in its own WHERE clause. Used in flattening decision making. DERBY-3301 reported wrong results from a nested WHERE EXISTS, but according to the derby optimizer docs this applies to a broader range of WHERE clauses in a WHERE EXISTS subquery. No WHERE EXISTS subquery with anohter subquery in it own WHERE clause can be flattened.
      Returns:
      true if this subquery is a WHERE EXISTS | ANY | IN subquery with a subquery in its own WHERE clause
      Throws:
      StandardException
    • getOrderByList

      public OrderByList getOrderByList()
      Get ORDER BY list (used to construct FROM_SUBQUERY only), cf. FromSubquery, for which this node is transient.
      Returns:
      order by list if specified, else null.
    • getOffset

      public ValueNode getOffset()
      Get OFFSET (used to construct FROM_SUBQUERY only), cf. FromSubquery, for which this node is transient.
      Returns:
      offset if specified, else null.
    • getFetchFirst

      public ValueNode getFetchFirst()
      Get FETCH FIRST (used to construct FROM_SUBQUERY only), cf. FromSubquery, for which this node is transient.
      Returns:
      fetch first if specified, else null.
    • hasJDBClimitClause

      public boolean hasJDBClimitClause()
      Return true if the offset/fetchFirst clauses were added by JDBC LIMIT escape syntax. This method is used to construct a FROM_SUBQUERY only, cf. FromSubquery, for which this node is transient.
      Returns:
      true if the JDBC limit/offset semantics (rather than the SQL Standard OFFSET/FETCH NEXT) semantics apply