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Sourcecode: postgresql-8.4 version File versions

var.c

/*-------------------------------------------------------------------------
 *
 * var.c
 *      Var node manipulation routines
 *
 * Note: for most purposes, PlaceHolderVar is considered a Var too,
 * even if its contained expression is variable-free.  Also, CurrentOfExpr
 * is treated as a Var for purposes of determining whether an expression
 * contains variables.
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/sysattr.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/prep.h"
#include "optimizer/var.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"


typedef struct
{
      Relids            varnos;
      int               sublevels_up;
} pull_varnos_context;

typedef struct
{
      int               var_location;
      int               sublevels_up;
} locate_var_of_level_context;

typedef struct
{
      int               var_location;
      int               relid;
      int               sublevels_up;
} locate_var_of_relation_context;

typedef struct
{
      int               min_varlevel;
      int               sublevels_up;
} find_minimum_var_level_context;

typedef struct
{
      List     *varlist;
      bool        includePlaceHolderVars;
} pull_var_clause_context;

typedef struct
{
      PlannerInfo *root;
      int               sublevels_up;
} flatten_join_alias_vars_context;

static bool pull_varnos_walker(Node *node,
                           pull_varnos_context *context);
static bool pull_varattnos_walker(Node *node, Bitmapset **varattnos);
static bool contain_var_clause_walker(Node *node, void *context);
static bool contain_vars_of_level_walker(Node *node, int *sublevels_up);
static bool locate_var_of_level_walker(Node *node,
                                                         locate_var_of_level_context *context);
static bool locate_var_of_relation_walker(Node *node,
                                                      locate_var_of_relation_context *context);
static bool find_minimum_var_level_walker(Node *node,
                                            find_minimum_var_level_context *context);
static bool pull_var_clause_walker(Node *node,
                                 pull_var_clause_context *context);
static Node *flatten_join_alias_vars_mutator(Node *node,
                                                flatten_join_alias_vars_context *context);
static Relids alias_relid_set(PlannerInfo *root, Relids relids);


/*
 * pull_varnos
 *          Create a set of all the distinct varnos present in a parsetree.
 *          Only varnos that reference level-zero rtable entries are considered.
 *
 * NOTE: this is used on not-yet-planned expressions.  It may therefore find
 * bare SubLinks, and if so it needs to recurse into them to look for uplevel
 * references to the desired rtable level!      But when we find a completed
 * SubPlan, we only need to look at the parameters passed to the subplan.
 */
Relids
pull_varnos(Node *node)
{
      pull_varnos_context context;

      context.varnos = NULL;
      context.sublevels_up = 0;

      /*
       * Must be prepared to start with a Query or a bare expression tree; if
       * it's a Query, we don't want to increment sublevels_up.
       */
      query_or_expression_tree_walker(node,
                                                      pull_varnos_walker,
                                                      (void *) &context,
                                                      0);

      return context.varnos;
}

static bool
pull_varnos_walker(Node *node, pull_varnos_context *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            Var            *var = (Var *) node;

            if (var->varlevelsup == context->sublevels_up)
                  context->varnos = bms_add_member(context->varnos, var->varno);
            return false;
      }
      if (IsA(node, CurrentOfExpr))
      {
            CurrentOfExpr *cexpr = (CurrentOfExpr *) node;

            if (context->sublevels_up == 0)
                  context->varnos = bms_add_member(context->varnos, cexpr->cvarno);
            return false;
      }
      if (IsA(node, PlaceHolderVar))
      {
            /*
             * Normally, we can just take the varnos in the contained expression.
             * But if it is variable-free, use the PHV's syntactic relids.
             */
            PlaceHolderVar *phv = (PlaceHolderVar *) node;
            pull_varnos_context subcontext;

            subcontext.varnos = NULL;
            subcontext.sublevels_up = context->sublevels_up;
            (void) pull_varnos_walker((Node *) phv->phexpr, &subcontext);

            if (bms_is_empty(subcontext.varnos) &&
                  phv->phlevelsup == context->sublevels_up)
                  context->varnos = bms_add_members(context->varnos, phv->phrels);
            else
                  context->varnos = bms_join(context->varnos, subcontext.varnos);
            return false;
      }
      if (IsA(node, Query))
      {
            /* Recurse into RTE subquery or not-yet-planned sublink subquery */
            bool        result;

            context->sublevels_up++;
            result = query_tree_walker((Query *) node, pull_varnos_walker,
                                                   (void *) context, 0);
            context->sublevels_up--;
            return result;
      }
      return expression_tree_walker(node, pull_varnos_walker,
                                                  (void *) context);
}


/*
 * pull_varattnos
 *          Find all the distinct attribute numbers present in an expression tree,
 *          and add them to the initial contents of *varattnos.
 *          Only Vars that reference RTE 1 of rtable level zero are considered.
 *
 * Attribute numbers are offset by FirstLowInvalidHeapAttributeNumber so that
 * we can include system attributes (e.g., OID) in the bitmap representation.
 *
 * Currently, this does not support subqueries nor expressions containing
 * references to multiple tables; not needed since it's only applied to
 * index expressions and predicates.
 */
void
pull_varattnos(Node *node, Bitmapset **varattnos)
{
      (void) pull_varattnos_walker(node, varattnos);
}

static bool
pull_varattnos_walker(Node *node, Bitmapset **varattnos)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            Var            *var = (Var *) node;

            Assert(var->varno == 1);
            *varattnos = bms_add_member(*varattnos,
                                     var->varattno - FirstLowInvalidHeapAttributeNumber);
            return false;
      }
      /* Should not find a subquery or subplan */
      Assert(!IsA(node, Query));
      Assert(!IsA(node, SubPlan));

      return expression_tree_walker(node, pull_varattnos_walker,
                                                  (void *) varattnos);
}


/*
 * contain_var_clause
 *      Recursively scan a clause to discover whether it contains any Var nodes
 *      (of the current query level).
 *
 *      Returns true if any varnode found.
 *
 * Does not examine subqueries, therefore must only be used after reduction
 * of sublinks to subplans!
 */
bool
contain_var_clause(Node *node)
{
      return contain_var_clause_walker(node, NULL);
}

static bool
contain_var_clause_walker(Node *node, void *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            if (((Var *) node)->varlevelsup == 0)
                  return true;            /* abort the tree traversal and return true */
            return false;
      }
      if (IsA(node, CurrentOfExpr))
            return true;
      if (IsA(node, PlaceHolderVar))
      {
            if (((PlaceHolderVar *) node)->phlevelsup == 0)
                  return true;            /* abort the tree traversal and return true */
            /* else fall through to check the contained expr */
      }
      return expression_tree_walker(node, contain_var_clause_walker, context);
}


/*
 * contain_vars_of_level
 *      Recursively scan a clause to discover whether it contains any Var nodes
 *      of the specified query level.
 *
 *      Returns true if any such Var found.
 *
 * Will recurse into sublinks.      Also, may be invoked directly on a Query.
 */
bool
contain_vars_of_level(Node *node, int levelsup)
{
      int               sublevels_up = levelsup;

      return query_or_expression_tree_walker(node,
                                                               contain_vars_of_level_walker,
                                                               (void *) &sublevels_up,
                                                               0);
}

static bool
contain_vars_of_level_walker(Node *node, int *sublevels_up)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            if (((Var *) node)->varlevelsup == *sublevels_up)
                  return true;            /* abort tree traversal and return true */
            return false;
      }
      if (IsA(node, CurrentOfExpr))
      {
            if (*sublevels_up == 0)
                  return true;
            return false;
      }
      if (IsA(node, PlaceHolderVar))
      {
            if (((PlaceHolderVar *) node)->phlevelsup == *sublevels_up)
                  return true;            /* abort the tree traversal and return true */
            /* else fall through to check the contained expr */
      }
      if (IsA(node, Query))
      {
            /* Recurse into subselects */
            bool        result;

            (*sublevels_up)++;
            result = query_tree_walker((Query *) node,
                                                   contain_vars_of_level_walker,
                                                   (void *) sublevels_up,
                                                   0);
            (*sublevels_up)--;
            return result;
      }
      return expression_tree_walker(node,
                                                  contain_vars_of_level_walker,
                                                  (void *) sublevels_up);
}


/*
 * locate_var_of_level
 *      Find the parse location of any Var of the specified query level.
 *
 * Returns -1 if no such Var is in the querytree, or if they all have
 * unknown parse location.  (The former case is probably caller error,
 * but we don't bother to distinguish it from the latter case.)
 *
 * Will recurse into sublinks.      Also, may be invoked directly on a Query.
 *
 * Note: it might seem appropriate to merge this functionality into
 * contain_vars_of_level, but that would complicate that function's API.
 * Currently, the only uses of this function are for error reporting,
 * and so shaving cycles probably isn't very important.
 */
int
locate_var_of_level(Node *node, int levelsup)
{
      locate_var_of_level_context context;

      context.var_location = -1;          /* in case we find nothing */
      context.sublevels_up = levelsup;

      (void) query_or_expression_tree_walker(node,
                                                               locate_var_of_level_walker,
                                                               (void *) &context,
                                                               0);

      return context.var_location;
}

static bool
locate_var_of_level_walker(Node *node,
                                       locate_var_of_level_context *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            Var      *var = (Var *) node;

            if (var->varlevelsup == context->sublevels_up &&
                  var->location >= 0)
            {
                  context->var_location = var->location;
                  return true;            /* abort tree traversal and return true */
            }
            return false;
      }
      if (IsA(node, CurrentOfExpr))
      {
            /* since CurrentOfExpr doesn't carry location, nothing we can do */
            return false;
      }
      /* No extra code needed for PlaceHolderVar; just look in contained expr */
      if (IsA(node, Query))
      {
            /* Recurse into subselects */
            bool        result;

            context->sublevels_up++;
            result = query_tree_walker((Query *) node,
                                                   locate_var_of_level_walker,
                                                   (void *) context,
                                                   0);
            context->sublevels_up--;
            return result;
      }
      return expression_tree_walker(node,
                                                  locate_var_of_level_walker,
                                                  (void *) context);
}


/*
 * locate_var_of_relation
 *      Find the parse location of any Var of the specified relation.
 *
 * Returns -1 if no such Var is in the querytree, or if they all have
 * unknown parse location.
 *
 * Will recurse into sublinks.      Also, may be invoked directly on a Query.
 */
int
locate_var_of_relation(Node *node, int relid, int levelsup)
{
      locate_var_of_relation_context context;

      context.var_location = -1;          /* in case we find nothing */
      context.relid = relid;
      context.sublevels_up = levelsup;

      (void) query_or_expression_tree_walker(node,
                                                               locate_var_of_relation_walker,
                                                               (void *) &context,
                                                               0);

      return context.var_location;
}

static bool
locate_var_of_relation_walker(Node *node,
                                            locate_var_of_relation_context *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            Var      *var = (Var *) node;

            if (var->varno == context->relid &&
                  var->varlevelsup == context->sublevels_up &&
                  var->location >= 0)
            {
                  context->var_location = var->location;
                  return true;            /* abort tree traversal and return true */
            }
            return false;
      }
      if (IsA(node, CurrentOfExpr))
      {
            /* since CurrentOfExpr doesn't carry location, nothing we can do */
            return false;
      }
      /* No extra code needed for PlaceHolderVar; just look in contained expr */
      if (IsA(node, Query))
      {
            /* Recurse into subselects */
            bool        result;

            context->sublevels_up++;
            result = query_tree_walker((Query *) node,
                                                   locate_var_of_relation_walker,
                                                   (void *) context,
                                                   0);
            context->sublevels_up--;
            return result;
      }
      return expression_tree_walker(node,
                                                  locate_var_of_relation_walker,
                                                  (void *) context);
}


/*
 * find_minimum_var_level
 *      Recursively scan a clause to find the lowest variable level it
 *      contains --- for example, zero is returned if there are any local
 *      variables, one if there are no local variables but there are
 *      one-level-up outer references, etc.  Subqueries are scanned to see
 *      if they possess relevant outer references.  (But any local variables
 *      within subqueries are not relevant.)
 *
 *      -1 is returned if the clause has no variables at all.
 *
 * Will recurse into sublinks.      Also, may be invoked directly on a Query.
 */
int
find_minimum_var_level(Node *node)
{
      find_minimum_var_level_context context;

      context.min_varlevel = -1;    /* signifies nothing found yet */
      context.sublevels_up = 0;

      (void) query_or_expression_tree_walker(node,
                                                               find_minimum_var_level_walker,
                                                               (void *) &context,
                                                               0);

      return context.min_varlevel;
}

static bool
find_minimum_var_level_walker(Node *node,
                                            find_minimum_var_level_context *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            int               varlevelsup = ((Var *) node)->varlevelsup;

            /* convert levelsup to frame of reference of original query */
            varlevelsup -= context->sublevels_up;
            /* ignore local vars of subqueries */
            if (varlevelsup >= 0)
            {
                  if (context->min_varlevel < 0 ||
                        context->min_varlevel > varlevelsup)
                  {
                        context->min_varlevel = varlevelsup;

                        /*
                         * As soon as we find a local variable, we can abort the tree
                         * traversal, since min_varlevel is then certainly 0.
                         */
                        if (varlevelsup == 0)
                              return true;
                  }
            }
      }
      if (IsA(node, CurrentOfExpr))
      {
            int               varlevelsup = 0;

            /* convert levelsup to frame of reference of original query */
            varlevelsup -= context->sublevels_up;
            /* ignore local vars of subqueries */
            if (varlevelsup >= 0)
            {
                  if (context->min_varlevel < 0 ||
                        context->min_varlevel > varlevelsup)
                  {
                        context->min_varlevel = varlevelsup;

                        /*
                         * As soon as we find a local variable, we can abort the tree
                         * traversal, since min_varlevel is then certainly 0.
                         */
                        if (varlevelsup == 0)
                              return true;
                  }
            }
      }

      /*
       * An Aggref must be treated like a Var of its level.  Normally we'd get
       * the same result from looking at the Vars in the aggregate's argument,
       * but this fails in the case of a Var-less aggregate call (COUNT(*)).
       */
      if (IsA(node, Aggref))
      {
            int               agglevelsup = ((Aggref *) node)->agglevelsup;

            /* convert levelsup to frame of reference of original query */
            agglevelsup -= context->sublevels_up;
            /* ignore local aggs of subqueries */
            if (agglevelsup >= 0)
            {
                  if (context->min_varlevel < 0 ||
                        context->min_varlevel > agglevelsup)
                  {
                        context->min_varlevel = agglevelsup;

                        /*
                         * As soon as we find a local aggregate, we can abort the tree
                         * traversal, since min_varlevel is then certainly 0.
                         */
                        if (agglevelsup == 0)
                              return true;
                  }
            }
      }
      /* Likewise, make sure PlaceHolderVar is treated correctly */
      if (IsA(node, PlaceHolderVar))
      {
            int               phlevelsup = ((PlaceHolderVar *) node)->phlevelsup;

            /* convert levelsup to frame of reference of original query */
            phlevelsup -= context->sublevels_up;
            /* ignore local vars of subqueries */
            if (phlevelsup >= 0)
            {
                  if (context->min_varlevel < 0 ||
                        context->min_varlevel > phlevelsup)
                  {
                        context->min_varlevel = phlevelsup;

                        /*
                         * As soon as we find a local variable, we can abort the tree
                         * traversal, since min_varlevel is then certainly 0.
                         */
                        if (phlevelsup == 0)
                              return true;
                  }
            }
      }
      if (IsA(node, Query))
      {
            /* Recurse into subselects */
            bool        result;

            context->sublevels_up++;
            result = query_tree_walker((Query *) node,
                                                   find_minimum_var_level_walker,
                                                   (void *) context,
                                                   0);
            context->sublevels_up--;
            return result;
      }
      return expression_tree_walker(node,
                                                  find_minimum_var_level_walker,
                                                  (void *) context);
}


/*
 * pull_var_clause
 *      Recursively pulls all Var nodes from an expression clause.
 *
 *      PlaceHolderVars are included too, if includePlaceHolderVars is true.
 *      If it isn't true, an error is thrown if any are found.
 *      Note that Vars within a PHV's expression are *not* included.
 *
 *      CurrentOfExpr nodes are *not* included.
 *
 *      Upper-level vars (with varlevelsup > 0) are not included.
 *      (These probably represent errors too, but we don't complain.)
 *
 *      Returns list of nodes found.  Note the nodes themselves are not
 *      copied, only referenced.
 *
 * Does not examine subqueries, therefore must only be used after reduction
 * of sublinks to subplans!
 */
List *
pull_var_clause(Node *node, bool includePlaceHolderVars)
{
      pull_var_clause_context context;

      context.varlist = NIL;
      context.includePlaceHolderVars = includePlaceHolderVars;

      pull_var_clause_walker(node, &context);
      return context.varlist;
}

static bool
pull_var_clause_walker(Node *node, pull_var_clause_context *context)
{
      if (node == NULL)
            return false;
      if (IsA(node, Var))
      {
            if (((Var *) node)->varlevelsup == 0)
                  context->varlist = lappend(context->varlist, node);
            return false;
      }
      if (IsA(node, PlaceHolderVar))
      {
            if (!context->includePlaceHolderVars)
                  elog(ERROR, "PlaceHolderVar found where not expected");
            if (((PlaceHolderVar *) node)->phlevelsup == 0)
                  context->varlist = lappend(context->varlist, node);
            /* we do NOT descend into the contained expression */
            return false;
      }
      return expression_tree_walker(node, pull_var_clause_walker,
                                                  (void *) context);
}


/*
 * flatten_join_alias_vars
 *      Replace Vars that reference JOIN outputs with references to the original
 *      relation variables instead.  This allows quals involving such vars to be
 *      pushed down.    Whole-row Vars that reference JOIN relations are expanded
 *      into RowExpr constructs that name the individual output Vars.  This
 *      is necessary since we will not scan the JOIN as a base relation, which
 *      is the only way that the executor can directly handle whole-row Vars.
 *
 * This also adjusts relid sets found in some expression node types to
 * substitute the contained base rels for any join relid.
 *
 * NOTE: this is used on not-yet-planned expressions.  We do not expect it
 * to be applied directly to a Query node.
 */
Node *
flatten_join_alias_vars(PlannerInfo *root, Node *node)
{
      flatten_join_alias_vars_context context;

      context.root = root;
      context.sublevels_up = 0;

      return flatten_join_alias_vars_mutator(node, &context);
}

static Node *
flatten_join_alias_vars_mutator(Node *node,
                                                flatten_join_alias_vars_context *context)
{
      if (node == NULL)
            return NULL;
      if (IsA(node, Var))
      {
            Var            *var = (Var *) node;
            RangeTblEntry *rte;
            Node     *newvar;

            /* No change unless Var belongs to a JOIN of the target level */
            if (var->varlevelsup != context->sublevels_up)
                  return node;            /* no need to copy, really */
            rte = rt_fetch(var->varno, context->root->parse->rtable);
            if (rte->rtekind != RTE_JOIN)
                  return node;
            if (var->varattno == InvalidAttrNumber)
            {
                  /* Must expand whole-row reference */
                  RowExpr    *rowexpr;
                  List     *fields = NIL;
                  AttrNumber  attnum;
                  ListCell   *l;

                  attnum = 0;
                  foreach(l, rte->joinaliasvars)
                  {
                        newvar = (Node *) lfirst(l);
                        attnum++;
                        /* Ignore dropped columns */
                        if (IsA(newvar, Const))
                              continue;

                        /*
                         * If we are expanding an alias carried down from an upper
                         * query, must adjust its varlevelsup fields.
                         */
                        if (context->sublevels_up != 0)
                        {
                              newvar = copyObject(newvar);
                              IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
                        }
                        /* Recurse in case join input is itself a join */
                        newvar = flatten_join_alias_vars_mutator(newvar, context);
                        fields = lappend(fields, newvar);
                  }
                  rowexpr = makeNode(RowExpr);
                  rowexpr->args = fields;
                  rowexpr->row_typeid = var->vartype;
                  rowexpr->row_format = COERCE_IMPLICIT_CAST;
                  rowexpr->colnames = NIL;
                  rowexpr->location = -1;

                  return (Node *) rowexpr;
            }

            /* Expand join alias reference */
            Assert(var->varattno > 0);
            newvar = (Node *) list_nth(rte->joinaliasvars, var->varattno - 1);

            /*
             * If we are expanding an alias carried down from an upper query, must
             * adjust its varlevelsup fields.
             */
            if (context->sublevels_up != 0)
            {
                  newvar = copyObject(newvar);
                  IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
            }
            /* Recurse in case join input is itself a join */
            return flatten_join_alias_vars_mutator(newvar, context);
      }
      if (IsA(node, PlaceHolderVar))
      {
            /* Copy the PlaceHolderVar node with correct mutation of subnodes */
            PlaceHolderVar *phv;

            phv = (PlaceHolderVar *) expression_tree_mutator(node,
                                                                   flatten_join_alias_vars_mutator,
                                                                                     (void *) context);
            /* now fix PlaceHolderVar's relid sets */
            if (phv->phlevelsup == context->sublevels_up)
            {
                  phv->phrels = alias_relid_set(context->root,
                                                              phv->phrels);
            }
            return (Node *) phv;
      }

      if (IsA(node, Query))
      {
            /* Recurse into RTE subquery or not-yet-planned sublink subquery */
            Query    *newnode;

            context->sublevels_up++;
            newnode = query_tree_mutator((Query *) node,
                                                       flatten_join_alias_vars_mutator,
                                                       (void *) context,
                                                       QTW_IGNORE_JOINALIASES);
            context->sublevels_up--;
            return (Node *) newnode;
      }
      /* Already-planned tree not supported */
      Assert(!IsA(node, SubPlan));
      /* Shouldn't need to handle these planner auxiliary nodes here */
      Assert(!IsA(node, SpecialJoinInfo));
      Assert(!IsA(node, PlaceHolderInfo));

      return expression_tree_mutator(node, flatten_join_alias_vars_mutator,
                                                   (void *) context);
}

/*
 * alias_relid_set: in a set of RT indexes, replace joins by their
 * underlying base relids
 */
static Relids
alias_relid_set(PlannerInfo *root, Relids relids)
{
      Relids            result = NULL;
      Relids            tmprelids;
      int               rtindex;

      tmprelids = bms_copy(relids);
      while ((rtindex = bms_first_member(tmprelids)) >= 0)
      {
            RangeTblEntry *rte = rt_fetch(rtindex, root->parse->rtable);

            if (rte->rtekind == RTE_JOIN)
                  result = bms_join(result, get_relids_for_join(root, rtindex));
            else
                  result = bms_add_member(result, rtindex);
      }
      bms_free(tmprelids);
      return result;
}

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