/src/postgres/src/backend/optimizer/util/var.c

Source
/*-------------------------------------------------------------------------
 *
 * 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) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/util/var.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

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


typedef struct
{
  Relids    varnos;
  PlannerInfo *root;
  int     sublevels_up;
} pull_varnos_context;

typedef struct
{
  Bitmapset  *varattnos;
  Index   varno;
} pull_varattnos_context;

typedef struct
{
  List     *vars;
  int     sublevels_up;
} pull_vars_context;

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

typedef struct
{
  List     *varlist;
  int     flags;
} pull_var_clause_context;

typedef struct
{
  PlannerInfo *root;      /* could be NULL! */
  Query    *query;      /* outer Query */
  int     sublevels_up;
  bool    possible_sublink; /* could aliases include a SubLink? */
  bool    inserted_sublink; /* have we inserted a SubLink? */
} flatten_join_alias_vars_context;

static bool pull_varnos_walker(Node *node,
                 pull_varnos_context *context);
static bool pull_varattnos_walker(Node *node, pull_varattnos_context *context);
static bool pull_vars_walker(Node *node, pull_vars_context *context);
static bool contain_var_clause_walker(Node *node, void *context);
static bool contain_vars_of_level_walker(Node *node, int *sublevels_up);
static bool contain_vars_returning_old_or_new_walker(Node *node, void *context);
static bool locate_var_of_level_walker(Node *node,
                     locate_var_of_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 Node *flatten_group_exprs_mutator(Node *node,
                     flatten_join_alias_vars_context *context);
static Node *mark_nullable_by_grouping(PlannerInfo *root, Node *newnode,
                     Var *oldvar);
static Node *add_nullingrels_if_needed(PlannerInfo *root, Node *newnode,
                     Var *oldvar);
static bool is_standard_join_alias_expression(Node *newnode, Var *oldvar);
static void adjust_standard_join_alias_expression(Node *newnode, Var *oldvar);
static Relids alias_relid_set(Query *query, 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.
 *
 * The result includes outer-join relids mentioned in Var.varnullingrels and
 * PlaceHolderVar.phnullingrels fields in the parsetree.
 *
 * "root" can be passed as NULL if it is not necessary to process
 * PlaceHolderVars.
 *
 * 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(PlannerInfo *root, Node *node)
{
  pull_varnos_context context;

  context.varnos = NULL;
  context.root = root;
  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,
                  &context,
                  0);

  return context.varnos;
}

/*
 * pull_varnos_of_level
 *    Create a set of all the distinct varnos present in a parsetree.
 *    Only Vars of the specified level are considered.
 */
Relids
pull_varnos_of_level(PlannerInfo *root, Node *node, int levelsup)
{
  pull_varnos_context context;

  context.varnos = NULL;
  context.root = root;
  context.sublevels_up = levelsup;

  /*
   * 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,
                  &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);
      context->varnos = bms_add_members(context->varnos,
                        var->varnullingrels);
    }
    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))
  {
    PlaceHolderVar *phv = (PlaceHolderVar *) node;

    /*
     * If a PlaceHolderVar is not of the target query level, ignore it,
     * instead recursing into its expression to see if it contains any
     * vars that are of the target level.  We'll also do that when the
     * caller doesn't pass a "root" pointer.  (We probably shouldn't see
     * PlaceHolderVars at all in such cases, but if we do, this is a
     * reasonable behavior.)
     */
    if (phv->phlevelsup == context->sublevels_up &&
      context->root != NULL)
    {
      /*
       * Ideally, the PHV's contribution to context->varnos is its
       * ph_eval_at set.  However, this code can be invoked before
       * that's been computed.  If we cannot find a PlaceHolderInfo,
       * fall back to the conservative assumption that the PHV will be
       * evaluated at its syntactic level (phv->phrels).
       *
       * Another problem is that a PlaceHolderVar can appear in quals or
       * tlists that have been translated for use in a child appendrel.
       * Typically such a PHV is a parameter expression sourced by some
       * other relation, so that the translation from parent appendrel
       * to child doesn't change its phrels, and we should still take
       * ph_eval_at at face value.  But in corner cases, the PHV's
       * original phrels can include the parent appendrel itself, in
       * which case the translated PHV will have the child appendrel in
       * phrels, and we must translate ph_eval_at to match.
       */
      PlaceHolderInfo *phinfo = NULL;

      if (phv->phlevelsup == 0)
      {
        if (phv->phid < context->root->placeholder_array_size)
          phinfo = context->root->placeholder_array[phv->phid];
      }
      if (phinfo == NULL)
      {
        /* No PlaceHolderInfo yet, use phrels */
        context->varnos = bms_add_members(context->varnos,
                          phv->phrels);
      }
      else if (bms_equal(phv->phrels, phinfo->ph_var->phrels))
      {
        /* Normal case: use ph_eval_at */
        context->varnos = bms_add_members(context->varnos,
                          phinfo->ph_eval_at);
      }
      else
      {
        /* Translated PlaceHolderVar: translate ph_eval_at to match */
        Relids    newevalat,
              delta;

        /* remove what was removed from phv->phrels ... */
        delta = bms_difference(phinfo->ph_var->phrels, phv->phrels);
        newevalat = bms_difference(phinfo->ph_eval_at, delta);
        /* ... then if that was in fact part of ph_eval_at ... */
        if (!bms_equal(newevalat, phinfo->ph_eval_at))
        {
          /* ... add what was added */
          delta = bms_difference(phv->phrels, phinfo->ph_var->phrels);
          newevalat = bms_join(newevalat, delta);
        }
        context->varnos = bms_join(context->varnos,
                       newevalat);
      }

      /*
       * In all three cases, include phnullingrels in the result.  We
       * don't worry about possibly needing to translate it, because
       * appendrels only translate varnos of baserels, not outer joins.
       */
      context->varnos = bms_add_members(context->varnos,
                        phv->phnullingrels);
      return false;    /* don't recurse into expression */
    }
  }
  else 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,
                   context, 0);
    context->sublevels_up--;
    return result;
  }
  return expression_tree_walker(node, pull_varnos_walker, 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 of the given varno and 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 unplanned subqueries; that is not needed
 * for current uses.  It will handle already-planned SubPlan nodes, though,
 * looking into only the "testexpr" and the "args" list.  (The subplan cannot
 * contain any other references to Vars of the current level.)
 */
void
pull_varattnos(Node *node, Index varno, Bitmapset **varattnos)
{
  pull_varattnos_context context;

  context.varattnos = *varattnos;
  context.varno = varno;

  (void) pull_varattnos_walker(node, &context);

  *varattnos = context.varattnos;
}

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

    if (var->varno == context->varno && var->varlevelsup == 0)
      context->varattnos =
        bms_add_member(context->varattnos,
                 var->varattno - FirstLowInvalidHeapAttributeNumber);
    return false;
  }

  /* Should not find an unplanned subquery */
  Assert(!IsA(node, Query));

  return expression_tree_walker(node, pull_varattnos_walker, context);
}


/*
 * pull_vars_of_level
 *    Create a list of all Vars (and PlaceHolderVars) referencing the
 *    specified query level in the given parsetree.
 *
 * Caution: the Vars are not copied, only linked into the list.
 */
List *
pull_vars_of_level(Node *node, int levelsup)
{
  pull_vars_context context;

  context.vars = NIL;
  context.sublevels_up = levelsup;

  /*
   * 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_vars_walker,
                  &context,
                  0);

  return context.vars;
}

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

    if (var->varlevelsup == context->sublevels_up)
      context->vars = lappend(context->vars, var);
    return false;
  }
  if (IsA(node, PlaceHolderVar))
  {
    PlaceHolderVar *phv = (PlaceHolderVar *) node;

    if (phv->phlevelsup == context->sublevels_up)
      context->vars = lappend(context->vars, phv);
    /* we don't want to look into the contained expression */
    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_vars_walker,
                   context, 0);
    context->sublevels_up--;
    return result;
  }
  return expression_tree_walker(node, pull_vars_walker, context);
}


/*
 * 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,
                       &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,
                   sublevels_up,
                   0);
    (*sublevels_up)--;
    return result;
  }
  return expression_tree_walker(node,
                  contain_vars_of_level_walker,
                  sublevels_up);
}


/*
 * contain_vars_returning_old_or_new
 *    Recursively scan a clause to discover whether it contains any Var nodes
 *    (of the current query level) whose varreturningtype is VAR_RETURNING_OLD
 *    or VAR_RETURNING_NEW.
 *
 *    Returns true if any found.
 *
 * Any ReturningExprs are also detected --- if an OLD/NEW Var was rewritten,
 * we still regard this as a clause that returns OLD/NEW values.
 *
 * Does not examine subqueries, therefore must only be used after reduction
 * of sublinks to subplans!
 */
bool
contain_vars_returning_old_or_new(Node *node)
{
  return contain_vars_returning_old_or_new_walker(node, NULL);
}

static bool
contain_vars_returning_old_or_new_walker(Node *node, void *context)
{
  if (node == NULL)
    return false;
  if (IsA(node, Var))
  {
    if (((Var *) node)->varlevelsup == 0 &&
      ((Var *) node)->varreturningtype != VAR_RETURNING_DEFAULT)
      return true;   /* abort the tree traversal and return true */
    return false;
  }
  if (IsA(node, ReturningExpr))
  {
    if (((ReturningExpr *) node)->retlevelsup == 0)
      return true;   /* abort the tree traversal and return true */
    return false;
  }
  return expression_tree_walker(node, contain_vars_returning_old_or_new_walker,
                  context);
}


/*
 * 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,
                       &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,
                   context,
                   0);
    context->sublevels_up--;
    return result;
  }
  return expression_tree_walker(node,
                  locate_var_of_level_walker,
                  context);
}


/*
 * pull_var_clause
 *    Recursively pulls all Var nodes from an expression clause.
 *
 *    Aggrefs are handled according to these bits in 'flags':
 *    PVC_INCLUDE_AGGREGATES    include Aggrefs in output list
 *    PVC_RECURSE_AGGREGATES    recurse into Aggref arguments
 *    neither flag        throw error if Aggref found
 *    Vars within an Aggref's expression are included in the result only
 *    when PVC_RECURSE_AGGREGATES is specified.
 *
 *    WindowFuncs are handled according to these bits in 'flags':
 *    PVC_INCLUDE_WINDOWFUNCS   include WindowFuncs in output list
 *    PVC_RECURSE_WINDOWFUNCS   recurse into WindowFunc arguments
 *    neither flag        throw error if WindowFunc found
 *    Vars within a WindowFunc's expression are included in the result only
 *    when PVC_RECURSE_WINDOWFUNCS is specified.
 *
 *    PlaceHolderVars are handled according to these bits in 'flags':
 *    PVC_INCLUDE_PLACEHOLDERS  include PlaceHolderVars in output list
 *    PVC_RECURSE_PLACEHOLDERS  recurse into PlaceHolderVar arguments
 *    neither flag        throw error if PlaceHolderVar found
 *    Vars within a PHV's expression are included in the result only
 *    when PVC_RECURSE_PLACEHOLDERS is specified.
 *
 *    GroupingFuncs are treated exactly like Aggrefs, and so do not need
 *    their own flag bits.
 *
 *    CurrentOfExpr nodes are ignored in all cases.
 *
 *    Upper-level vars (with varlevelsup > 0) should not be seen here,
 *    likewise for upper-level Aggrefs and PlaceHolderVars.
 *
 *    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, int flags)
{
  pull_var_clause_context context;

  /* Assert that caller has not specified inconsistent flags */
  Assert((flags & (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES))
       != (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES));
  Assert((flags & (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS))
       != (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS));
  Assert((flags & (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS))
       != (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS));

  context.varlist = NIL;
  context.flags = flags;

  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)
      elog(ERROR, "Upper-level Var found where not expected");
    context->varlist = lappend(context->varlist, node);
    return false;
  }
  else if (IsA(node, Aggref))
  {
    if (((Aggref *) node)->agglevelsup != 0)
      elog(ERROR, "Upper-level Aggref found where not expected");
    if (context->flags & PVC_INCLUDE_AGGREGATES)
    {
      context->varlist = lappend(context->varlist, node);
      /* we do NOT descend into the contained expression */
      return false;
    }
    else if (context->flags & PVC_RECURSE_AGGREGATES)
    {
      /* fall through to recurse into the aggregate's arguments */
    }
    else
      elog(ERROR, "Aggref found where not expected");
  }
  else if (IsA(node, GroupingFunc))
  {
    if (((GroupingFunc *) node)->agglevelsup != 0)
      elog(ERROR, "Upper-level GROUPING found where not expected");
    if (context->flags & PVC_INCLUDE_AGGREGATES)
    {
      context->varlist = lappend(context->varlist, node);
      /* we do NOT descend into the contained expression */
      return false;
    }
    else if (context->flags & PVC_RECURSE_AGGREGATES)
    {
      /* fall through to recurse into the GroupingFunc's arguments */
    }
    else
      elog(ERROR, "GROUPING found where not expected");
  }
  else if (IsA(node, WindowFunc))
  {
    /* WindowFuncs have no levelsup field to check ... */
    if (context->flags & PVC_INCLUDE_WINDOWFUNCS)
    {
      context->varlist = lappend(context->varlist, node);
      /* we do NOT descend into the contained expressions */
      return false;
    }
    else if (context->flags & PVC_RECURSE_WINDOWFUNCS)
    {
      /* fall through to recurse into the windowfunc's arguments */
    }
    else
      elog(ERROR, "WindowFunc found where not expected");
  }
  else if (IsA(node, PlaceHolderVar))
  {
    if (((PlaceHolderVar *) node)->phlevelsup != 0)
      elog(ERROR, "Upper-level PlaceHolderVar found where not expected");
    if (context->flags & PVC_INCLUDE_PLACEHOLDERS)
    {
      context->varlist = lappend(context->varlist, node);
      /* we do NOT descend into the contained expression */
      return false;
    }
    else if (context->flags & PVC_RECURSE_PLACEHOLDERS)
    {
      /* fall through to recurse into the placeholder's expression */
    }
    else
      elog(ERROR, "PlaceHolderVar found where not expected");
  }
  return expression_tree_walker(node, pull_var_clause_walker, 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+OJ rels for any join relid.
 *
 * If a JOIN contains sub-selects that have been flattened, its join alias
 * entries might now be arbitrary expressions, not just Vars.  This affects
 * this function in two important ways.  First, we might find ourselves
 * inserting SubLink expressions into subqueries, and we must make sure that
 * their Query.hasSubLinks fields get set to true if so.  If there are any
 * SubLinks in the join alias lists, the outer Query should already have
 * hasSubLinks = true, so this is only relevant to un-flattened subqueries.
 * Second, we have to preserve any varnullingrels info attached to the
 * alias Vars we're replacing.  If the replacement expression is a Var or
 * PlaceHolderVar or constructed from those, we can just add the
 * varnullingrels bits to the existing nullingrels field(s); otherwise
 * we have to add a PlaceHolderVar wrapper.
 */
Node *
flatten_join_alias_vars(PlannerInfo *root, Query *query, Node *node)
{
  flatten_join_alias_vars_context context;

  /*
   * We do not expect this to be applied to the whole Query, only to
   * expressions or LATERAL subqueries.  Hence, if the top node is a Query,
   * it's okay to immediately increment sublevels_up.
   */
  Assert(node != (Node *) query);

  context.root = root;
  context.query = query;
  context.sublevels_up = 0;
  /* flag whether join aliases could possibly contain SubLinks */
  context.possible_sublink = query->hasSubLinks;
  /* if hasSubLinks is already true, no need to work hard */
  context.inserted_sublink = query->hasSubLinks;

  return flatten_join_alias_vars_mutator(node, &context);
}

/*
 * flatten_join_alias_for_parser
 *
 * This variant of flatten_join_alias_vars is used by the parser, to expand
 * join alias Vars before checking GROUP BY validity.  In that case we lack
 * a root structure.  Fortunately, we'd only need the root for making
 * PlaceHolderVars.  We can avoid making PlaceHolderVars in the parser's
 * usage because it won't be dealing with arbitrary expressions: so long as
 * adjust_standard_join_alias_expression can handle everything the parser
 * would make as a join alias expression, we're OK.
 *
 * The "node" might be part of a sub-query of the Query whose join alias
 * Vars are to be expanded.  "sublevels_up" indicates how far below the
 * given query we are starting.
 */
Node *
flatten_join_alias_for_parser(Query *query, Node *node, int sublevels_up)
{
  flatten_join_alias_vars_context context;

  /*
   * We do not expect this to be applied to the whole Query, only to
   * expressions or LATERAL subqueries.  Hence, if the top node is a Query,
   * it's okay to immediately increment sublevels_up.
   */
  Assert(node != (Node *) query);

  context.root = NULL;
  context.query = query;
  context.sublevels_up = sublevels_up;
  /* flag whether join aliases could possibly contain SubLinks */
  context.possible_sublink = query->hasSubLinks;
  /* if hasSubLinks is already true, no need to work hard */
  context.inserted_sublink = query->hasSubLinks;

  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->query->rtable);
    if (rte->rtekind != RTE_JOIN)
      return node;
    if (var->varattno == InvalidAttrNumber)
    {
      /* Must expand whole-row reference */
      RowExpr    *rowexpr;
      List     *fields = NIL;
      List     *colnames = NIL;
      ListCell   *lv;
      ListCell   *ln;

      Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
      forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
      {
        newvar = (Node *) lfirst(lv);
        /* Ignore dropped columns */
        if (newvar == NULL)
          continue;
        newvar = copyObject(newvar);

        /*
         * If we are expanding an alias carried down from an upper
         * query, must adjust its varlevelsup fields.
         */
        if (context->sublevels_up != 0)
          IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
        /* Preserve original Var's location, if possible */
        if (IsA(newvar, Var))
          ((Var *) newvar)->location = var->location;
        /* Recurse in case join input is itself a join */
        /* (also takes care of setting inserted_sublink if needed) */
        newvar = flatten_join_alias_vars_mutator(newvar, context);
        fields = lappend(fields, newvar);
        /* We need the names of non-dropped columns, too */
        colnames = lappend(colnames, copyObject((Node *) lfirst(ln)));
      }
      rowexpr = makeNode(RowExpr);
      rowexpr->args = fields;
      rowexpr->row_typeid = var->vartype;
      rowexpr->row_format = COERCE_IMPLICIT_CAST;
      /* vartype will always be RECORDOID, so we always need colnames */
      rowexpr->colnames = colnames;
      rowexpr->location = var->location;

      /* Lastly, add any varnullingrels to the replacement expression */
      return add_nullingrels_if_needed(context->root, (Node *) rowexpr,
                       var);
    }

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

    /*
     * If we are expanding an alias carried down from an upper query, must
     * adjust its varlevelsup fields.
     */
    if (context->sublevels_up != 0)
      IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);

    /* Preserve original Var's location, if possible */
    if (IsA(newvar, Var))
      ((Var *) newvar)->location = var->location;

    /* Recurse in case join input is itself a join */
    newvar = flatten_join_alias_vars_mutator(newvar, context);

    /* Detect if we are adding a sublink to query */
    if (context->possible_sublink && !context->inserted_sublink)
      context->inserted_sublink = checkExprHasSubLink(newvar);

    /* Lastly, add any varnullingrels to the replacement expression */
    return add_nullingrels_if_needed(context->root, newvar, var);
  }
  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,
                             context);
    /* now fix PlaceHolderVar's relid sets */
    if (phv->phlevelsup == context->sublevels_up)
    {
      phv->phrels = alias_relid_set(context->query,
                      phv->phrels);
      /* we *don't* change phnullingrels */
    }
    return (Node *) phv;
  }

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

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

  return expression_tree_mutator(node, flatten_join_alias_vars_mutator, context);
}

/*
 * flatten_group_exprs
 *    Replace Vars that reference GROUP outputs with the underlying grouping
 *    expressions.
 *
 * We have to preserve any varnullingrels info attached to the group Vars we're
 * replacing.  If the replacement expression is a Var or PlaceHolderVar or
 * constructed from those, we can just add the varnullingrels bits to the
 * existing nullingrels field(s); otherwise we have to add a PlaceHolderVar
 * wrapper.
 *
 * NOTE: root may be passed as NULL, which is why we have to pass the Query
 * separately.  We need the root itself only for preserving varnullingrels.
 * Callers can safely pass NULL if preserving varnullingrels is unnecessary for
 * their specific use case (e.g., deparsing source text, or scanning for
 * volatile functions), or if it is already guaranteed that the query cannot
 * contain grouping sets.
 */
Node *
flatten_group_exprs(PlannerInfo *root, Query *query, Node *node)
{
  flatten_join_alias_vars_context context;

  /*
   * We do not expect this to be applied to the whole Query, only to
   * expressions or LATERAL subqueries.  Hence, if the top node is a Query,
   * it's okay to immediately increment sublevels_up.
   */
  Assert(node != (Node *) query);

  context.root = root;
  context.query = query;
  context.sublevels_up = 0;
  /* flag whether grouping expressions could possibly contain SubLinks */
  context.possible_sublink = query->hasSubLinks;
  /* if hasSubLinks is already true, no need to work hard */
  context.inserted_sublink = query->hasSubLinks;

  return flatten_group_exprs_mutator(node, &context);
}

static Node *
flatten_group_exprs_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 the GROUP of the target level */
    if (var->varlevelsup != context->sublevels_up)
      return node;   /* no need to copy, really */
    rte = rt_fetch(var->varno, context->query->rtable);
    if (rte->rtekind != RTE_GROUP)
      return node;

    /* Expand group exprs reference */
    Assert(var->varattno > 0);
    newvar = (Node *) list_nth(rte->groupexprs, var->varattno - 1);
    Assert(newvar != NULL);
    newvar = copyObject(newvar);

    /*
     * If we are expanding an expr carried down from an upper query, must
     * adjust its varlevelsup fields.
     */
    if (context->sublevels_up != 0)
      IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);

    /* Preserve original Var's location, if possible */
    if (IsA(newvar, Var))
      ((Var *) newvar)->location = var->location;

    /* Detect if we are adding a sublink to query */
    if (context->possible_sublink && !context->inserted_sublink)
      context->inserted_sublink = checkExprHasSubLink(newvar);

    /* Lastly, add any varnullingrels to the replacement expression */
    return mark_nullable_by_grouping(context->root, newvar, var);
  }

  if (IsA(node, Aggref))
  {
    Aggref     *agg = (Aggref *) node;

    if ((int) agg->agglevelsup == context->sublevels_up)
    {
      /*
       * If we find an aggregate call of the original level, do not
       * recurse into its normal arguments, ORDER BY arguments, or
       * filter; there are no grouped vars there.  But we should check
       * direct arguments as though they weren't in an aggregate.
       */
      agg = copyObject(agg);
      agg->aggdirectargs = (List *)
        flatten_group_exprs_mutator((Node *) agg->aggdirectargs, context);

      return (Node *) agg;
    }

    /*
     * We can skip recursing into aggregates of higher levels altogether,
     * since they could not possibly contain Vars of concern to us (see
     * transformAggregateCall).  We do need to look at aggregates of lower
     * levels, however.
     */
    if ((int) agg->agglevelsup > context->sublevels_up)
      return node;
  }

  if (IsA(node, GroupingFunc))
  {
    GroupingFunc *grp = (GroupingFunc *) node;

    /*
     * If we find a GroupingFunc node of the original or higher level, do
     * not recurse into its arguments; there are no grouped vars there.
     */
    if ((int) grp->agglevelsup >= context->sublevels_up)
      return node;
  }

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

    context->sublevels_up++;
    save_inserted_sublink = context->inserted_sublink;
    context->inserted_sublink = ((Query *) node)->hasSubLinks;
    newnode = query_tree_mutator((Query *) node,
                   flatten_group_exprs_mutator,
                   context,
                   QTW_IGNORE_GROUPEXPRS);
    newnode->hasSubLinks |= context->inserted_sublink;
    context->inserted_sublink = save_inserted_sublink;
    context->sublevels_up--;
    return (Node *) newnode;
  }

  return expression_tree_mutator(node, flatten_group_exprs_mutator,
                   context);
}

/*
 * Add oldvar's varnullingrels, if any, to a flattened grouping expression.
 * The newnode has been copied, so we can modify it freely.
 */
static Node *
mark_nullable_by_grouping(PlannerInfo *root, Node *newnode, Var *oldvar)
{
  Relids    relids;

  if (root == NULL)
    return newnode;
  if (oldvar->varnullingrels == NULL)
    return newnode;     /* nothing to do */

  Assert(bms_equal(oldvar->varnullingrels,
           bms_make_singleton(root->group_rtindex)));

  relids = pull_varnos_of_level(root, newnode, oldvar->varlevelsup);

  if (!bms_is_empty(relids))
  {
    /*
     * If the newnode is not variable-free, we set the nullingrels of Vars
     * or PHVs that are contained in the expression.  This is not really
     * 'correct' in theory, because it is the whole expression that can be
     * nullable by grouping sets, not its individual vars.  But it works
     * in practice, because what we need is that the expression can be
     * somehow distinguished from the same expression in ECs, and marking
     * its vars is sufficient for this purpose.
     */
    newnode = add_nulling_relids(newnode,
                   relids,
                   oldvar->varnullingrels);
  }
  else            /* variable-free? */
  {
    /*
     * If the newnode is variable-free and does not contain volatile
     * functions or set-returning functions, it can be treated as a member
     * of EC that is redundant.  So wrap it in a new PlaceHolderVar to
     * carry the nullingrels.  Otherwise we do not bother to make any
     * changes.
     *
     * Aggregate functions and window functions are not allowed in
     * grouping expressions.
     */
    Assert(!contain_agg_clause(newnode));
    Assert(!contain_window_function(newnode));

    if (!contain_volatile_functions(newnode) &&
      !expression_returns_set(newnode))
    {
      PlaceHolderVar *newphv;
      Relids    phrels;

      phrels = get_relids_in_jointree((Node *) root->parse->jointree,
                      true, false);
      Assert(!bms_is_empty(phrels));

      newphv = make_placeholder_expr(root, (Expr *) newnode, phrels);
      /* newphv has zero phlevelsup and NULL phnullingrels; fix it */
      newphv->phlevelsup = oldvar->varlevelsup;
      newphv->phnullingrels = bms_copy(oldvar->varnullingrels);
      newnode = (Node *) newphv;
    }
  }

  return newnode;
}

/*
 * Add oldvar's varnullingrels, if any, to a flattened join alias expression.
 * The newnode has been copied, so we can modify it freely.
 */
static Node *
add_nullingrels_if_needed(PlannerInfo *root, Node *newnode, Var *oldvar)
{
  if (oldvar->varnullingrels == NULL)
    return newnode;     /* nothing to do */
  /* If possible, do it by adding to existing nullingrel fields */
  if (is_standard_join_alias_expression(newnode, oldvar))
    adjust_standard_join_alias_expression(newnode, oldvar);
  else if (root)
  {
    /*
     * We can insert a PlaceHolderVar to carry the nullingrels.  However,
     * deciding where to evaluate the PHV is slightly tricky.  We first
     * try to evaluate it at the natural semantic level of the new
     * expression; but if that expression is variable-free, fall back to
     * evaluating it at the join that the oldvar is an alias Var for.
     */
    PlaceHolderVar *newphv;
    Index   levelsup = oldvar->varlevelsup;
    Relids    phrels = pull_varnos_of_level(root, newnode, levelsup);

    if (bms_is_empty(phrels)) /* variable-free? */
    {
      if (levelsup != 0) /* this won't work otherwise */
        elog(ERROR, "unsupported join alias expression");
      phrels = get_relids_for_join(root->parse, oldvar->varno);
      /* If it's an outer join, eval below not above the join */
      phrels = bms_del_member(phrels, oldvar->varno);
      Assert(!bms_is_empty(phrels));
    }
    newphv = make_placeholder_expr(root, (Expr *) newnode, phrels);
    /* newphv has zero phlevelsup and NULL phnullingrels; fix it */
    newphv->phlevelsup = levelsup;
    newphv->phnullingrels = bms_copy(oldvar->varnullingrels);
    newnode = (Node *) newphv;
  }
  else
  {
    /* ooops, we're missing support for something the parser can make */
    elog(ERROR, "unsupported join alias expression");
  }
  return newnode;
}

/*
 * Check to see if we can insert nullingrels into this join alias expression
 * without use of a separate PlaceHolderVar.
 *
 * This will handle Vars, PlaceHolderVars, and implicit-coercion and COALESCE
 * expressions built from those.  This coverage needs to handle anything
 * that the parser would put into joinaliasvars.
 */
static bool
is_standard_join_alias_expression(Node *newnode, Var *oldvar)
{
  if (newnode == NULL)
    return false;
  if (IsA(newnode, Var) &&
    ((Var *) newnode)->varlevelsup == oldvar->varlevelsup)
    return true;
  else if (IsA(newnode, PlaceHolderVar) &&
       ((PlaceHolderVar *) newnode)->phlevelsup == oldvar->varlevelsup)
    return true;
  else if (IsA(newnode, FuncExpr))
  {
    FuncExpr   *fexpr = (FuncExpr *) newnode;

    /*
     * We need to assume that the function wouldn't produce non-NULL from
     * NULL, which is reasonable for implicit coercions but otherwise not
     * so much.  (Looking at its strictness is likely overkill, and anyway
     * it would cause us to fail if someone forgot to mark an implicit
     * coercion as strict.)
     */
    if (fexpr->funcformat != COERCE_IMPLICIT_CAST ||
      fexpr->args == NIL)
      return false;

    /*
     * Examine only the first argument --- coercions might have additional
     * arguments that are constants.
     */
    return is_standard_join_alias_expression(linitial(fexpr->args), oldvar);
  }
  else if (IsA(newnode, RelabelType))
  {
    RelabelType *relabel = (RelabelType *) newnode;

    /* This definitely won't produce non-NULL from NULL */
    return is_standard_join_alias_expression((Node *) relabel->arg, oldvar);
  }
  else if (IsA(newnode, CoerceViaIO))
  {
    CoerceViaIO *iocoerce = (CoerceViaIO *) newnode;

    /* This definitely won't produce non-NULL from NULL */
    return is_standard_join_alias_expression((Node *) iocoerce->arg, oldvar);
  }
  else if (IsA(newnode, ArrayCoerceExpr))
  {
    ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) newnode;

    /* This definitely won't produce non-NULL from NULL (at array level) */
    return is_standard_join_alias_expression((Node *) acoerce->arg, oldvar);
  }
  else if (IsA(newnode, CoalesceExpr))
  {
    CoalesceExpr *cexpr = (CoalesceExpr *) newnode;
    ListCell   *lc;

    Assert(cexpr->args != NIL);
    foreach(lc, cexpr->args)
    {
      if (!is_standard_join_alias_expression(lfirst(lc), oldvar))
        return false;
    }
    return true;
  }
  else
    return false;
}

/*
 * Insert nullingrels into an expression accepted by
 * is_standard_join_alias_expression.
 */
static void
adjust_standard_join_alias_expression(Node *newnode, Var *oldvar)
{
  if (IsA(newnode, Var) &&
    ((Var *) newnode)->varlevelsup == oldvar->varlevelsup)
  {
    Var      *newvar = (Var *) newnode;

    newvar->varnullingrels = bms_add_members(newvar->varnullingrels,
                         oldvar->varnullingrels);
  }
  else if (IsA(newnode, PlaceHolderVar) &&
       ((PlaceHolderVar *) newnode)->phlevelsup == oldvar->varlevelsup)
  {
    PlaceHolderVar *newphv = (PlaceHolderVar *) newnode;

    newphv->phnullingrels = bms_add_members(newphv->phnullingrels,
                        oldvar->varnullingrels);
  }
  else if (IsA(newnode, FuncExpr))
  {
    FuncExpr   *fexpr = (FuncExpr *) newnode;

    adjust_standard_join_alias_expression(linitial(fexpr->args), oldvar);
  }
  else if (IsA(newnode, RelabelType))
  {
    RelabelType *relabel = (RelabelType *) newnode;

    adjust_standard_join_alias_expression((Node *) relabel->arg, oldvar);
  }
  else if (IsA(newnode, CoerceViaIO))
  {
    CoerceViaIO *iocoerce = (CoerceViaIO *) newnode;

    adjust_standard_join_alias_expression((Node *) iocoerce->arg, oldvar);
  }
  else if (IsA(newnode, ArrayCoerceExpr))
  {
    ArrayCoerceExpr *acoerce = (ArrayCoerceExpr *) newnode;

    adjust_standard_join_alias_expression((Node *) acoerce->arg, oldvar);
  }
  else if (IsA(newnode, CoalesceExpr))
  {
    CoalesceExpr *cexpr = (CoalesceExpr *) newnode;
    ListCell   *lc;

    Assert(cexpr->args != NIL);
    foreach(lc, cexpr->args)
    {
      adjust_standard_join_alias_expression(lfirst(lc), oldvar);
    }
  }
  else
    Assert(false);
}

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

  rtindex = -1;
  while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
  {
    RangeTblEntry *rte = rt_fetch(rtindex, query->rtable);

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

Coverage Report

Created: 2026-08-13 07:12