var.c

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/*-------------------------------------------------------------------------
 *
 * 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) 1996-2013, 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/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
{
    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;
    PVCAggregateBehavior aggbehavior;
    PVCPlaceHolderBehavior phbehavior;
} pull_var_clause_context;

typedef struct
{
    PlannerInfo *root;
    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 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 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;
}

/*
 * 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(Node *node, int levelsup)
{
    pull_varnos_context context;

    context.varnos = NULL;
    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,
                                    (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 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,
                                  (void *) 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,
                                    (void *) &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,
                                   (void *) context, 0);
        context->sublevels_up--;
        return result;
    }
    return expression_tree_walker(node, pull_vars_walker,
                                  (void *) 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,
                                           (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);
}


/*
 * pull_var_clause
 *    Recursively pulls all Var nodes from an expression clause.
 *
 *    Aggrefs are handled according to 'aggbehavior':
 *      PVC_REJECT_AGGREGATES       throw error if Aggref found
 *      PVC_INCLUDE_AGGREGATES      include Aggrefs in output list
 *      PVC_RECURSE_AGGREGATES      recurse into Aggref arguments
 *    Vars within an Aggref's expression are included only in the last case.
 *
 *    PlaceHolderVars are handled according to 'phbehavior':
 *      PVC_REJECT_PLACEHOLDERS     throw error if PlaceHolderVar found
 *      PVC_INCLUDE_PLACEHOLDERS    include PlaceHolderVars in output list
 *      PVC_RECURSE_PLACEHOLDERS    recurse into PlaceHolderVar arguments
 *    Vars within a PHV's expression are included only in the last case.
 *
 *    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, PVCAggregateBehavior aggbehavior,
                PVCPlaceHolderBehavior phbehavior)
{
    pull_var_clause_context context;

    context.varlist = NIL;
    context.aggbehavior = aggbehavior;
    context.phbehavior = phbehavior;

    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");
        switch (context->aggbehavior)
        {
            case PVC_REJECT_AGGREGATES:
                elog(ERROR, "Aggref found where not expected");
                break;
            case PVC_INCLUDE_AGGREGATES:
                context->varlist = lappend(context->varlist, node);
                /* we do NOT descend into the contained expression */
                return false;
            case PVC_RECURSE_AGGREGATES:
                /* ignore the aggregate, look at its argument instead */
                break;
        }
    }
    else if (IsA(node, PlaceHolderVar))
    {
        if (((PlaceHolderVar *) node)->phlevelsup != 0)
            elog(ERROR, "Upper-level PlaceHolderVar found where not expected");
        switch (context->phbehavior)
        {
            case PVC_REJECT_PLACEHOLDERS:
                elog(ERROR, "PlaceHolderVar found where not expected");
                break;
            case PVC_INCLUDE_PLACEHOLDERS:
                context->varlist = lappend(context->varlist, node);
                /* we do NOT descend into the contained expression */
                return false;
            case PVC_RECURSE_PLACEHOLDERS:
                /* ignore the placeholder, look at its argument instead */
                break;
        }
    }
    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.
 *
 * 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 one important way: 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.
 *
 * NOTE: this is used on not-yet-planned expressions.  We do not expect it
 * to be applied directly to the whole Query, so if we see a Query to start
 * with, we do want to increment sublevels_up (this occurs for LATERAL
 * subqueries).
 */
Node *
flatten_join_alias_vars(PlannerInfo *root, Node *node)
{
    flatten_join_alias_vars_context context;

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

            attnum = 0;
            Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
            forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
            {
                newvar = (Node *) lfirst(lv);
                attnum++;
                /* Ignore dropped columns */
                if (IsA(newvar, Const))
                    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;
            rowexpr->colnames = colnames;
            rowexpr->location = var->location;

            return (Node *) rowexpr;
        }

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

        return newvar;
    }
    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;
        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,
                                     (void *) 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));
    /* Shouldn't need to handle these planner auxiliary nodes here */
    Assert(!IsA(node, SpecialJoinInfo));
    Assert(!IsA(node, LateralJoinInfo));
    Assert(!IsA(node, PlaceHolderInfo));
    Assert(!IsA(node, MinMaxAggInfo));

    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;
}