/*-------------------------------------------------------------------------
*
* deparse.c
* Query deparser for postgres_fdw
*
* This file includes functions that examine query WHERE clauses to see
* whether they're safe to send to the remote server for execution, as
* well as functions to construct the query text to be sent. The latter
* functionality is annoyingly duplicative of ruleutils.c, but there are
* enough special considerations that it seems best to keep this separate.
* One saving grace is that we only need deparse logic for node types that
* we consider safe to send.
*
* We assume that the remote session's search_path is exactly "pg_catalog",
* and thus we need schema-qualify all and only names outside pg_catalog.
*
* We do not consider that it is ever safe to send COLLATE expressions to
* the remote server: it might not have the same collation names we do.
* (Later we might consider it safe to send COLLATE "C", but even that would
* fail on old remote servers.) An expression is considered safe to send only
* if all collations used in it are traceable to Var(s) of the foreign table.
* That implies that if the remote server gets a different answer than we do,
* the foreign table's columns are not marked with collations that match the
* remote table's columns, which we can consider to be user error.
*
* Portions Copyright (c) 2012-2015, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/postgres_fdw/deparse.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "postgres_fdw.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/transam.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/var.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
/*
* Global context for foreign_expr_walker's search of an expression tree.
*/
typedef struct foreign_glob_cxt
{
PlannerInfo *root; /* global planner state */
RelOptInfo *foreignrel; /* the foreign relation we are planning for */
} foreign_glob_cxt;
/*
* Local (per-tree-level) context for foreign_expr_walker's search.
* This is concerned with identifying collations used in the expression.
*/
typedef enum
{
FDW_COLLATE_NONE, /* expression is of a noncollatable type */
FDW_COLLATE_SAFE, /* collation derives from a foreign Var */
FDW_COLLATE_UNSAFE /* collation derives from something else */
} FDWCollateState;
typedef struct foreign_loc_cxt
{
Oid collation; /* OID of current collation, if any */
FDWCollateState state; /* state of current collation choice */
} foreign_loc_cxt;
/*
* Context for deparseExpr
*/
typedef struct deparse_expr_cxt
{
PlannerInfo *root; /* global planner state */
RelOptInfo *foreignrel; /* the foreign relation we are planning for */
StringInfo buf; /* output buffer to append to */
List **params_list; /* exprs that will become remote Params */
} deparse_expr_cxt;
/*
* Functions to determine whether an expression can be evaluated safely on
* remote server.
*/
static bool foreign_expr_walker(Node *node,
foreign_glob_cxt *glob_cxt,
foreign_loc_cxt *outer_cxt);
static bool is_builtin(Oid procid);
/*
* Functions to construct string representation of a node tree.
*/
static void deparseTargetList(StringInfo buf,
PlannerInfo *root,
Index rtindex,
Relation rel,
Bitmapset *attrs_used,
List **retrieved_attrs);
static void deparseReturningList(StringInfo buf, PlannerInfo *root,
Index rtindex, Relation rel,
bool trig_after_row,
List *returningList,
List **retrieved_attrs);
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
PlannerInfo *root);
static void deparseRelation(StringInfo buf, Relation rel);
static void deparseExpr(Expr *expr, deparse_expr_cxt *context);
static void deparseVar(Var *node, deparse_expr_cxt *context);
static void deparseConst(Const *node, deparse_expr_cxt *context);
static void deparseParam(Param *node, deparse_expr_cxt *context);
static void deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context);
static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
deparse_expr_cxt *context);
static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
static void printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
deparse_expr_cxt *context);
static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
deparse_expr_cxt *context);
/*
* Examine each qual clause in input_conds, and classify them into two groups,
* which are returned as two lists:
* - remote_conds contains expressions that can be evaluated remotely
* - local_conds contains expressions that can't be evaluated remotely
*/
void
classifyConditions(PlannerInfo *root,
RelOptInfo *baserel,
List *input_conds,
List **remote_conds,
List **local_conds)
{
ListCell *lc;
*remote_conds = NIL;
*local_conds = NIL;
foreach(lc, input_conds)
{
RestrictInfo *ri = (RestrictInfo *) lfirst(lc);
if (is_foreign_expr(root, baserel, ri->clause))
*remote_conds = lappend(*remote_conds, ri);
else
*local_conds = lappend(*local_conds, ri);
}
}
/*
* Returns true if given expr is safe to evaluate on the foreign server.
*/
bool
is_foreign_expr(PlannerInfo *root,
RelOptInfo *baserel,
Expr *expr)
{
foreign_glob_cxt glob_cxt;
foreign_loc_cxt loc_cxt;
/*
* Check that the expression consists of nodes that are safe to execute
* remotely.
*/
glob_cxt.root = root;
glob_cxt.foreignrel = baserel;
loc_cxt.collation = InvalidOid;
loc_cxt.state = FDW_COLLATE_NONE;
if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt))
return false;
/* Expressions examined here should be boolean, ie noncollatable */
Assert(loc_cxt.collation == InvalidOid);
Assert(loc_cxt.state == FDW_COLLATE_NONE);
/*
* An expression which includes any mutable functions can't be sent over
* because its result is not stable. For example, sending now() remote
* side could cause confusion from clock offsets. Future versions might
* be able to make this choice with more granularity. (We check this last
* because it requires a lot of expensive catalog lookups.)
*/
if (contain_mutable_functions((Node *) expr))
return false;
/* OK to evaluate on the remote server */
return true;
}
/*
* Check if expression is safe to execute remotely, and return true if so.
*
* In addition, *outer_cxt is updated with collation information.
*
* We must check that the expression contains only node types we can deparse,
* that all types/functions/operators are safe to send (which we approximate
* as being built-in), and that all collations used in the expression derive
* from Vars of the foreign table. Because of the latter, the logic is
* pretty close to assign_collations_walker() in parse_collate.c, though we
* can assume here that the given expression is valid.
*/
static bool
foreign_expr_walker(Node *node,
foreign_glob_cxt *glob_cxt,
foreign_loc_cxt *outer_cxt)
{
bool check_type = true;
foreign_loc_cxt inner_cxt;
Oid collation;
FDWCollateState state;
/* Need do nothing for empty subexpressions */
if (node == NULL)
return true;
/* Set up inner_cxt for possible recursion to child nodes */
inner_cxt.collation = InvalidOid;
inner_cxt.state = FDW_COLLATE_NONE;
switch (nodeTag(node))
{
case T_Var:
{
Var *var = (Var *) node;
/*
* If the Var is from the foreign table, we consider its
* collation (if any) safe to use. If it is from another
* table, we treat its collation the same way as we would a
* Param's collation, ie it's not safe for it to have a
* non-default collation.
*/
if (var->varno == glob_cxt->foreignrel->relid &&
var->varlevelsup == 0)
{
/* Var belongs to foreign table */
/*
* System columns other than ctid should not be sent to
* the remote, since we don't make any effort to ensure
* that local and remote values match (tableoid, in
* particular, almost certainly doesn't match).
*/
if (var->varattno < 0 &&
var->varattno != SelfItemPointerAttributeNumber)
return false;
/* Else check the collation */
collation = var->varcollid;
state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
}
else
{
/* Var belongs to some other table */
if (var->varcollid != InvalidOid &&
var->varcollid != DEFAULT_COLLATION_OID)
return false;
/* We can consider that it doesn't set collation */
collation = InvalidOid;
state = FDW_COLLATE_NONE;
}
}
break;
case T_Const:
{
Const *c = (Const *) node;
/*
* If the constant has nondefault collation, either it's of a
* non-builtin type, or it reflects folding of a CollateExpr;
* either way, it's unsafe to send to the remote.
*/
if (c->constcollid != InvalidOid &&
c->constcollid != DEFAULT_COLLATION_OID)
return false;
/* Otherwise, we can consider that it doesn't set collation */
collation = InvalidOid;
state = FDW_COLLATE_NONE;
}
break;
case T_Param:
{
Param *p = (Param *) node;
/*
* Collation handling is same as for Consts.
*/
if (p->paramcollid != InvalidOid &&
p->paramcollid != DEFAULT_COLLATION_OID)
return false;
collation = InvalidOid;
state = FDW_COLLATE_NONE;
}
break;
case T_ArrayRef:
{
ArrayRef *ar = (ArrayRef *) node;
/* Assignment should not be in restrictions. */
if (ar->refassgnexpr != NULL)
return false;
/*
* Recurse to remaining subexpressions. Since the array
* subscripts must yield (noncollatable) integers, they won't
* affect the inner_cxt state.
*/
if (!foreign_expr_walker((Node *) ar->refupperindexpr,
glob_cxt, &inner_cxt))
return false;
if (!foreign_expr_walker((Node *) ar->reflowerindexpr,
glob_cxt, &inner_cxt))
return false;
if (!foreign_expr_walker((Node *) ar->refexpr,
glob_cxt, &inner_cxt))
return false;
/*
* Array subscripting should yield same collation as input,
* but for safety use same logic as for function nodes.
*/
collation = ar->refcollid;
if (collation == InvalidOid)
state = FDW_COLLATE_NONE;
else if (inner_cxt.state == FDW_COLLATE_SAFE &&
collation == inner_cxt.collation)
state = FDW_COLLATE_SAFE;
else
state = FDW_COLLATE_UNSAFE;
}
break;
case T_FuncExpr:
{
FuncExpr *fe = (FuncExpr *) node;
/*
* If function used by the expression is not built-in, it
* can't be sent to remote because it might have incompatible
* semantics on remote side.
*/
if (!is_builtin(fe->funcid))
return false;
/*
* Recurse to input subexpressions.
*/
if (!foreign_expr_walker((Node *) fe->args,
glob_cxt, &inner_cxt))
return false;
/*
* If function's input collation is not derived from a foreign
* Var, it can't be sent to remote.
*/
if (fe->inputcollid == InvalidOid)
/* OK, inputs are all noncollatable */ ;
else if (inner_cxt.state != FDW_COLLATE_SAFE ||
fe->inputcollid != inner_cxt.collation)
return false;
/*
* Detect whether node is introducing a collation not derived
* from a foreign Var. (If so, we just mark it unsafe for now
* rather than immediately returning false, since the parent
* node might not care.)
*/
collation = fe->funccollid;
if (collation == InvalidOid)
state = FDW_COLLATE_NONE;
else if (inner_cxt.state == FDW_COLLATE_SAFE &&
collation == inner_cxt.collation)
state = FDW_COLLATE_SAFE;
else
state = FDW_COLLATE_UNSAFE;
}
break;
case T_OpExpr:
case T_DistinctExpr: /* struct-equivalent to OpExpr */
{
OpExpr *oe = (OpExpr *) node;
/*
* Similarly, only built-in operators can be sent to remote.
* (If the operator is, surely its underlying function is
* too.)
*/
if (!is_builtin(oe->opno))
return false;
/*
* Recurse to input subexpressions.
*/
if (!foreign_expr_walker((Node *) oe->args,
glob_cxt, &inner_cxt))
return false;
/*
* If operator's input collation is not derived from a foreign
* Var, it can't be sent to remote.
*/
if (oe->inputcollid == InvalidOid)
/* OK, inputs are all noncollatable */ ;
else if (inner_cxt.state != FDW_COLLATE_SAFE ||
oe->inputcollid != inner_cxt.collation)
return false;
/* Result-collation handling is same as for functions */
collation = oe->opcollid;
if (collation == InvalidOid)
state = FDW_COLLATE_NONE;
else if (inner_cxt.state == FDW_COLLATE_SAFE &&
collation == inner_cxt.collation)
state = FDW_COLLATE_SAFE;
else
state = FDW_COLLATE_UNSAFE;
}
break;
case T_ScalarArrayOpExpr:
{
ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;
/*
* Again, only built-in operators can be sent to remote.
*/
if (!is_builtin(oe->opno))
return false;
/*
* Recurse to input subexpressions.
*/
if (!foreign_expr_walker((Node *) oe->args,
glob_cxt, &inner_cxt))
return false;
/*
* If operator's input collation is not derived from a foreign
* Var, it can't be sent to remote.
*/
if (oe->inputcollid == InvalidOid)
/* OK, inputs are all noncollatable */ ;
else if (inner_cxt.state != FDW_COLLATE_SAFE ||
oe->inputcollid != inner_cxt.collation)
return false;
/* Output is always boolean and so noncollatable. */
collation = InvalidOid;
state = FDW_COLLATE_NONE;
}
break;
case T_RelabelType:
{
RelabelType *r = (RelabelType *) node;
/*
* Recurse to input subexpression.
*/
if (!foreign_expr_walker((Node *) r->arg,
glob_cxt, &inner_cxt))
return false;
/*
* RelabelType must not introduce a collation not derived from
* an input foreign Var.
*/
collation = r->resultcollid;
if (collation == InvalidOid)
state = FDW_COLLATE_NONE;
else if (inner_cxt.state == FDW_COLLATE_SAFE &&
collation == inner_cxt.collation)
state = FDW_COLLATE_SAFE;
else
state = FDW_COLLATE_UNSAFE;
}
break;
case T_BoolExpr:
{
BoolExpr *b = (BoolExpr *) node;
/*
* Recurse to input subexpressions.
*/
if (!foreign_expr_walker((Node *) b->args,
glob_cxt, &inner_cxt))
return false;
/* Output is always boolean and so noncollatable. */
collation = InvalidOid;
state = FDW_COLLATE_NONE;
}
break;
case T_NullTest:
{
NullTest *nt = (NullTest *) node;
/*
* Recurse to input subexpressions.
*/
if (!foreign_expr_walker((Node *) nt->arg,
glob_cxt, &inner_cxt))
return false;
/* Output is always boolean and so noncollatable. */
collation = InvalidOid;
state = FDW_COLLATE_NONE;
}
break;
case T_ArrayExpr:
{
ArrayExpr *a = (ArrayExpr *) node;
/*
* Recurse to input subexpressions.
*/
if (!foreign_expr_walker((Node *) a->elements,
glob_cxt, &inner_cxt))
return false;
/*
* ArrayExpr must not introduce a collation not derived from
* an input foreign Var.
*/
collation = a->array_collid;
if (collation == InvalidOid)
state = FDW_COLLATE_NONE;
else if (inner_cxt.state == FDW_COLLATE_SAFE &&
collation == inner_cxt.collation)
state = FDW_COLLATE_SAFE;
else
state = FDW_COLLATE_UNSAFE;
}
break;
case T_List:
{
List *l = (List *) node;
ListCell *lc;
/*
* Recurse to component subexpressions.
*/
foreach(lc, l)
{
if (!foreign_expr_walker((Node *) lfirst(lc),
glob_cxt, &inner_cxt))
return false;
}
/*
* When processing a list, collation state just bubbles up
* from the list elements.
*/
collation = inner_cxt.collation;
state = inner_cxt.state;
/* Don't apply exprType() to the list. */
check_type = false;
}
break;
default:
/*
* If it's anything else, assume it's unsafe. This list can be
* expanded later, but don't forget to add deparse support below.
*/
return false;
}
/*
* If result type of given expression is not built-in, it can't be sent to
* remote because it might have incompatible semantics on remote side.
*/
if (check_type && !is_builtin(exprType(node)))
return false;
/*
* Now, merge my collation information into my parent's state.
*/
if (state > outer_cxt->state)
{
/* Override previous parent state */
outer_cxt->collation = collation;
outer_cxt->state = state;
}
else if (state == outer_cxt->state)
{
/* Merge, or detect error if there's a collation conflict */
switch (state)
{
case FDW_COLLATE_NONE:
/* Nothing + nothing is still nothing */
break;
case FDW_COLLATE_SAFE:
if (collation != outer_cxt->collation)
{
/*
* Non-default collation always beats default.
*/
if (outer_cxt->collation == DEFAULT_COLLATION_OID)
{
/* Override previous parent state */
outer_cxt->collation = collation;
}
else if (collation != DEFAULT_COLLATION_OID)
{
/*
* Conflict; show state as indeterminate. We don't
* want to "return false" right away, since parent
* node might not care about collation.
*/
outer_cxt->state = FDW_COLLATE_UNSAFE;
}
}
break;
case FDW_COLLATE_UNSAFE:
/* We're still conflicted ... */
break;
}
}
/* It looks OK */
return true;
}
/*
* Return true if given object is one of PostgreSQL's built-in objects.
*
* We use FirstBootstrapObjectId as the cutoff, so that we only consider
* objects with hand-assigned OIDs to be "built in", not for instance any
* function or type defined in the information_schema.
*
* Our constraints for dealing with types are tighter than they are for
* functions or operators: we want to accept only types that are in pg_catalog,
* else format_type might incorrectly fail to schema-qualify their names.
* (This could be fixed with some changes to format_type, but for now there's
* no need.) Thus we must exclude information_schema types.
*
* XXX there is a problem with this, which is that the set of built-in
* objects expands over time. Something that is built-in to us might not
* be known to the remote server, if it's of an older version. But keeping
* track of that would be a huge exercise.
*/
static bool
is_builtin(Oid oid)
{
return (oid < FirstBootstrapObjectId);
}
/*
* Construct a simple SELECT statement that retrieves desired columns
* of the specified foreign table, and append it to "buf". The output
* contains just "SELECT ... FROM tablename".
*
* We also create an integer List of the columns being retrieved, which is
* returned to *retrieved_attrs.
*/
void
deparseSelectSql(StringInfo buf,
PlannerInfo *root,
RelOptInfo *baserel,
Bitmapset *attrs_used,
List **retrieved_attrs)
{
RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
Relation rel;
/*
* Core code already has some lock on each rel being planned, so we can
* use NoLock here.
*/
rel = heap_open(rte->relid, NoLock);
/*
* Construct SELECT list
*/
appendStringInfoString(buf, "SELECT ");
deparseTargetList(buf, root, baserel->relid, rel, attrs_used,
retrieved_attrs);
/*
* Construct FROM clause
*/
appendStringInfoString(buf, " FROM ");
deparseRelation(buf, rel);
heap_close(rel, NoLock);
}
/*
* Emit a target list that retrieves the columns specified in attrs_used.
* This is used for both SELECT and RETURNING targetlists.
*
* The tlist text is appended to buf, and we also create an integer List
* of the columns being retrieved, which is returned to *retrieved_attrs.
*/
static void
deparseTargetList(StringInfo buf,
PlannerInfo *root,
Index rtindex,
Relation rel,
Bitmapset *attrs_used,
List **retrieved_attrs)
{
TupleDesc tupdesc = RelationGetDescr(rel);
bool have_wholerow;
bool first;
int i;
*retrieved_attrs = NIL;
/* If there's a whole-row reference, we'll need all the columns. */
have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
attrs_used);
first = true;
for (i = 1; i <= tupdesc->natts; i++)
{
Form_pg_attribute attr = tupdesc->attrs[i - 1];
/* Ignore dropped attributes. */
if (attr->attisdropped)
continue;
if (have_wholerow ||
bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
attrs_used))
{
if (!first)
appendStringInfoString(buf, ", ");
first = false;
deparseColumnRef(buf, rtindex, i, root);
*retrieved_attrs = lappend_int(*retrieved_attrs, i);
}
}
/*
* Add ctid if needed. We currently don't support retrieving any other
* system columns.
*/
if (bms_is_member(SelfItemPointerAttributeNumber - FirstLowInvalidHeapAttributeNumber,
attrs_used))
{
if (!first)
appendStringInfoString(buf, ", ");
first = false;
appendStringInfoString(buf, "ctid");
*retrieved_attrs = lappend_int(*retrieved_attrs,
SelfItemPointerAttributeNumber);
}
/* Don't generate bad syntax if no undropped columns */
if (first)
appendStringInfoString(buf, "NULL");
}
/*
* Deparse WHERE clauses in given list of RestrictInfos and append them to buf.
*
* baserel is the foreign table we're planning for.
*
* If no WHERE clause already exists in the buffer, is_first should be true.
*
* If params is not NULL, it receives a list of Params and other-relation Vars
* used in the clauses; these values must be transmitted to the remote server
* as parameter values.
*
* If params is NULL, we're generating the query for EXPLAIN purposes,
* so Params and other-relation Vars should be replaced by dummy values.
*/
void
appendWhereClause(StringInfo buf,
PlannerInfo *root,
RelOptInfo *baserel,
List *exprs,
bool is_first,
List **params)
{
deparse_expr_cxt context;
int nestlevel;
ListCell *lc;
if (params)
*params = NIL; /* initialize result list to empty */
/* Set up context struct for recursion */
context.root = root;
context.foreignrel = baserel;
context.buf = buf;
context.params_list = params;
/* Make sure any constants in the exprs are printed portably */
nestlevel = set_transmission_modes();
foreach(lc, exprs)
{
RestrictInfo *ri = (RestrictInfo *) lfirst(lc);
/* Connect expressions with "AND" and parenthesize each condition. */
if (is_first)
appendStringInfoString(buf, " WHERE ");
else
appendStringInfoString(buf, " AND ");
appendStringInfoChar(buf, '(');
deparseExpr(ri->clause, &context);
appendStringInfoChar(buf, ')');
is_first = false;
}
reset_transmission_modes(nestlevel);
}
/*
* deparse remote INSERT statement
*
* The statement text is appended to buf, and we also create an integer List
* of the columns being retrieved by RETURNING (if any), which is returned
* to *retrieved_attrs.
*/
void
deparseInsertSql(StringInfo buf, PlannerInfo *root,
Index rtindex, Relation rel,
List *targetAttrs, bool doNothing,
List *returningList, List **retrieved_attrs)
{
AttrNumber pindex;
bool first;
ListCell *lc;
appendStringInfoString(buf, "INSERT INTO ");
deparseRelation(buf, rel);
if (targetAttrs)
{
appendStringInfoChar(buf, '(');
first = true;
foreach(lc, targetAttrs)
{
int attnum = lfirst_int(lc);
if (!first)
appendStringInfoString(buf, ", ");
first = false;
deparseColumnRef(buf, rtindex, attnum, root);
}
appendStringInfoString(buf, ") VALUES (");
pindex = 1;
first = true;
foreach(lc, targetAttrs)
{
if (!first)
appendStringInfoString(buf, ", ");
first = false;
appendStringInfo(buf, "$%d", pindex);
pindex++;
}
appendStringInfoChar(buf, ')');
}
else
appendStringInfoString(buf, " DEFAULT VALUES");
if (doNothing)
appendStringInfoString(buf, " ON CONFLICT DO NOTHING");
deparseReturningList(buf, root, rtindex, rel,
rel->trigdesc && rel->trigdesc->trig_insert_after_row,
returningList, retrieved_attrs);
}
/*
* deparse remote UPDATE statement
*
* The statement text is appended to buf, and we also create an integer List
* of the columns being retrieved by RETURNING (if any), which is returned
* to *retrieved_attrs.
*/
void
deparseUpdateSql(StringInfo buf, PlannerInfo *root,
Index rtindex, Relation rel,
List *targetAttrs, List *returningList,
List **retrieved_attrs)
{
AttrNumber pindex;
bool first;
ListCell *lc;
appendStringInfoString(buf, "UPDATE ");
deparseRelation(buf, rel);
appendStringInfoString(buf, " SET ");
pindex = 2; /* ctid is always the first param */
first = true;
foreach(lc, targetAttrs)
{
int attnum = lfirst_int(lc);
if (!first)
appendStringInfoString(buf, ", ");
first = false;
deparseColumnRef(buf, rtindex, attnum, root);
appendStringInfo(buf, " = $%d", pindex);
pindex++;
}
appendStringInfoString(buf, " WHERE ctid = $1");
deparseReturningList(buf, root, rtindex, rel,
rel->trigdesc && rel->trigdesc->trig_update_after_row,
returningList, retrieved_attrs);
}
/*
* deparse remote DELETE statement
*
* The statement text is appended to buf, and we also create an integer List
* of the columns being retrieved by RETURNING (if any), which is returned
* to *retrieved_attrs.
*/
void
deparseDeleteSql(StringInfo buf, PlannerInfo *root,
Index rtindex, Relation rel,
List *returningList,
List **retrieved_attrs)
{
appendStringInfoString(buf, "DELETE FROM ");
deparseRelation(buf, rel);
appendStringInfoString(buf, " WHERE ctid = $1");
deparseReturningList(buf, root, rtindex, rel,
rel->trigdesc && rel->trigdesc->trig_delete_after_row,
returningList, retrieved_attrs);
}
/*
* Add a RETURNING clause, if needed, to an INSERT/UPDATE/DELETE.
*/
static void
deparseReturningList(StringInfo buf, PlannerInfo *root,
Index rtindex, Relation rel,
bool trig_after_row,
List *returningList,
List **retrieved_attrs)
{
Bitmapset *attrs_used = NULL;
if (trig_after_row)
{
/* whole-row reference acquires all non-system columns */
attrs_used =
bms_make_singleton(0 - FirstLowInvalidHeapAttributeNumber);
}
if (returningList != NIL)
{
/*
* We need the attrs, non-system and system, mentioned in the local
* query's RETURNING list.
*/
pull_varattnos((Node *) returningList, rtindex,
&attrs_used);
}
if (attrs_used != NULL)
{
appendStringInfoString(buf, " RETURNING ");
deparseTargetList(buf, root, rtindex, rel, attrs_used,
retrieved_attrs);
}
else
*retrieved_attrs = NIL;
}
/*
* Construct SELECT statement to acquire size in blocks of given relation.
*
* Note: we use local definition of block size, not remote definition.
* This is perhaps debatable.
*
* Note: pg_relation_size() exists in 8.1 and later.
*/
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
StringInfoData relname;
/* We'll need the remote relation name as a literal. */
initStringInfo(&relname);
deparseRelation(&relname, rel);
appendStringInfoString(buf, "SELECT pg_catalog.pg_relation_size(");
deparseStringLiteral(buf, relname.data);
appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
}
/*
* Construct SELECT statement to acquire sample rows of given relation.
*
* SELECT command is appended to buf, and list of columns retrieved
* is returned to *retrieved_attrs.
*/
void
deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
{
Oid relid = RelationGetRelid(rel);
TupleDesc tupdesc = RelationGetDescr(rel);
int i;
char *colname;
List *options;
ListCell *lc;
bool first = true;
*retrieved_attrs = NIL;
appendStringInfoString(buf, "SELECT ");
for (i = 0; i < tupdesc->natts; i++)
{
/* Ignore dropped columns. */
if (tupdesc->attrs[i]->attisdropped)
continue;
if (!first)
appendStringInfoString(buf, ", ");
first = false;
/* Use attribute name or column_name option. */
colname = NameStr(tupdesc->attrs[i]->attname);
options = GetForeignColumnOptions(relid, i + 1);
foreach(lc, options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "column_name") == 0)
{
colname = defGetString(def);
break;
}
}
appendStringInfoString(buf, quote_identifier(colname));
*retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
}
/* Don't generate bad syntax for zero-column relation. */
if (first)
appendStringInfoString(buf, "NULL");
/*
* Construct FROM clause
*/
appendStringInfoString(buf, " FROM ");
deparseRelation(buf, rel);
}
/*
* Construct name to use for given column, and emit it into buf.
* If it has a column_name FDW option, use that instead of attribute name.
*/
static void
deparseColumnRef(StringInfo buf, int varno, int varattno, PlannerInfo *root)
{
RangeTblEntry *rte;
char *colname = NULL;
List *options;
ListCell *lc;
/* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
Assert(!IS_SPECIAL_VARNO(varno));
/* Get RangeTblEntry from array in PlannerInfo. */
rte = planner_rt_fetch(varno, root);
/*
* If it's a column of a foreign table, and it has the column_name FDW
* option, use that value.
*/
options = GetForeignColumnOptions(rte->relid, varattno);
foreach(lc, options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "column_name") == 0)
{
colname = defGetString(def);
break;
}
}
/*
* If it's a column of a regular table or it doesn't have column_name FDW
* option, use attribute name.
*/
if (colname == NULL)
colname = get_relid_attribute_name(rte->relid, varattno);
appendStringInfoString(buf, quote_identifier(colname));
}
/*
* Append remote name of specified foreign table to buf.
* Use value of table_name FDW option (if any) instead of relation's name.
* Similarly, schema_name FDW option overrides schema name.
*/
static void
deparseRelation(StringInfo buf, Relation rel)
{
ForeignTable *table;
const char *nspname = NULL;
const char *relname = NULL;
ListCell *lc;
/* obtain additional catalog information. */
table = GetForeignTable(RelationGetRelid(rel));
/*
* Use value of FDW options if any, instead of the name of object itself.
*/
foreach(lc, table->options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "schema_name") == 0)
nspname = defGetString(def);
else if (strcmp(def->defname, "table_name") == 0)
relname = defGetString(def);
}
/*
* Note: we could skip printing the schema name if it's pg_catalog, but
* that doesn't seem worth the trouble.
*/
if (nspname == NULL)
nspname = get_namespace_name(RelationGetNamespace(rel));
if (relname == NULL)
relname = RelationGetRelationName(rel);
appendStringInfo(buf, "%s.%s",
quote_identifier(nspname), quote_identifier(relname));
}
/*
* Append a SQL string literal representing "val" to buf.
*/
void
deparseStringLiteral(StringInfo buf, const char *val)
{
const char *valptr;
/*
* Rather than making assumptions about the remote server's value of
* standard_conforming_strings, always use E'foo' syntax if there are any
* backslashes. This will fail on remote servers before 8.1, but those
* are long out of support.
*/
if (strchr(val, '\\') != NULL)
appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
appendStringInfoChar(buf, '\'');
for (valptr = val; *valptr; valptr++)
{
char ch = *valptr;
if (SQL_STR_DOUBLE(ch, true))
appendStringInfoChar(buf, ch);
appendStringInfoChar(buf, ch);
}
appendStringInfoChar(buf, '\'');
}
/*
* Deparse given expression into context->buf.
*
* This function must support all the same node types that foreign_expr_walker
* accepts.
*
* Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
* scheme: anything more complex than a Var, Const, function call or cast
* should be self-parenthesized.
*/
static void
deparseExpr(Expr *node, deparse_expr_cxt *context)
{
if (node == NULL)
return;
switch (nodeTag(node))
{
case T_Var:
deparseVar((Var *) node, context);
break;
case T_Const:
deparseConst((Const *) node, context);
break;
case T_Param:
deparseParam((Param *) node, context);
break;
case T_ArrayRef:
deparseArrayRef((ArrayRef *) node, context);
break;
case T_FuncExpr:
deparseFuncExpr((FuncExpr *) node, context);
break;
case T_OpExpr:
deparseOpExpr((OpExpr *) node, context);
break;
case T_DistinctExpr:
deparseDistinctExpr((DistinctExpr *) node, context);
break;
case T_ScalarArrayOpExpr:
deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
break;
case T_RelabelType:
deparseRelabelType((RelabelType *) node, context);
break;
case T_BoolExpr:
deparseBoolExpr((BoolExpr *) node, context);
break;
case T_NullTest:
deparseNullTest((NullTest *) node, context);
break;
case T_ArrayExpr:
deparseArrayExpr((ArrayExpr *) node, context);
break;
default:
elog(ERROR, "unsupported expression type for deparse: %d",
(int) nodeTag(node));
break;
}
}
/*
* Deparse given Var node into context->buf.
*
* If the Var belongs to the foreign relation, just print its remote name.
* Otherwise, it's effectively a Param (and will in fact be a Param at
* run time). Handle it the same way we handle plain Params --- see
* deparseParam for comments.
*/
static void
deparseVar(Var *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
if (node->varno == context->foreignrel->relid &&
node->varlevelsup == 0)
{
/* Var belongs to foreign table */
deparseColumnRef(buf, node->varno, node->varattno, context->root);
}
else
{
/* Treat like a Param */
if (context->params_list)
{
int pindex = 0;
ListCell *lc;
/* find its index in params_list */
foreach(lc, *context->params_list)
{
pindex++;
if (equal(node, (Node *) lfirst(lc)))
break;
}
if (lc == NULL)
{
/* not in list, so add it */
pindex++;
*context->params_list = lappend(*context->params_list, node);
}
printRemoteParam(pindex, node->vartype, node->vartypmod, context);
}
else
{
printRemotePlaceholder(node->vartype, node->vartypmod, context);
}
}
}
/*
* Deparse given constant value into context->buf.
*
* This function has to be kept in sync with ruleutils.c's get_const_expr.
*/
static void
deparseConst(Const *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
Oid typoutput;
bool typIsVarlena;
char *extval;
bool isfloat = false;
bool needlabel;
if (node->constisnull)
{
appendStringInfoString(buf, "NULL");
appendStringInfo(buf, "::%s",
format_type_with_typemod(node->consttype,
node->consttypmod));
return;
}
getTypeOutputInfo(node->consttype,
&typoutput, &typIsVarlena);
extval = OidOutputFunctionCall(typoutput, node->constvalue);
switch (node->consttype)
{
case INT2OID:
case INT4OID:
case INT8OID:
case OIDOID:
case FLOAT4OID:
case FLOAT8OID:
case NUMERICOID:
{
/*
* No need to quote unless it's a special value such as 'NaN'.
* See comments in get_const_expr().
*/
if (strspn(extval, "0123456789+-eE.") == strlen(extval))
{
if (extval[0] == '+' || extval[0] == '-')
appendStringInfo(buf, "(%s)", extval);
else
appendStringInfoString(buf, extval);
if (strcspn(extval, "eE.") != strlen(extval))
isfloat = true; /* it looks like a float */
}
else
appendStringInfo(buf, "'%s'", extval);
}
break;
case BITOID:
case VARBITOID:
appendStringInfo(buf, "B'%s'", extval);
break;
case BOOLOID:
if (strcmp(extval, "t") == 0)
appendStringInfoString(buf, "true");
else
appendStringInfoString(buf, "false");
break;
default:
deparseStringLiteral(buf, extval);
break;
}
/*
* Append ::typename unless the constant will be implicitly typed as the
* right type when it is read in.
*
* XXX this code has to be kept in sync with the behavior of the parser,
* especially make_const.
*/
switch (node->consttype)
{
case BOOLOID:
case INT4OID:
case UNKNOWNOID:
needlabel = false;
break;
case NUMERICOID:
needlabel = !isfloat || (node->consttypmod >= 0);
break;
default:
needlabel = true;
break;
}
if (needlabel)
appendStringInfo(buf, "::%s",
format_type_with_typemod(node->consttype,
node->consttypmod));
}
/*
* Deparse given Param node.
*
* If we're generating the query "for real", add the Param to
* context->params_list if it's not already present, and then use its index
* in that list as the remote parameter number. During EXPLAIN, there's
* no need to identify a parameter number.
*/
static void
deparseParam(Param *node, deparse_expr_cxt *context)
{
if (context->params_list)
{
int pindex = 0;
ListCell *lc;
/* find its index in params_list */
foreach(lc, *context->params_list)
{
pindex++;
if (equal(node, (Node *) lfirst(lc)))
break;
}
if (lc == NULL)
{
/* not in list, so add it */
pindex++;
*context->params_list = lappend(*context->params_list, node);
}
printRemoteParam(pindex, node->paramtype, node->paramtypmod, context);
}
else
{
printRemotePlaceholder(node->paramtype, node->paramtypmod, context);
}
}
/*
* Deparse an array subscript expression.
*/
static void
deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
ListCell *lowlist_item;
ListCell *uplist_item;
/* Always parenthesize the expression. */
appendStringInfoChar(buf, '(');
/*
* Deparse referenced array expression first. If that expression includes
* a cast, we have to parenthesize to prevent the array subscript from
* being taken as typename decoration. We can avoid that in the typical
* case of subscripting a Var, but otherwise do it.
*/
if (IsA(node->refexpr, Var))
deparseExpr(node->refexpr, context);
else
{
appendStringInfoChar(buf, '(');
deparseExpr(node->refexpr, context);
appendStringInfoChar(buf, ')');
}
/* Deparse subscript expressions. */
lowlist_item = list_head(node->reflowerindexpr); /* could be NULL */
foreach(uplist_item, node->refupperindexpr)
{
appendStringInfoChar(buf, '[');
if (lowlist_item)
{
deparseExpr(lfirst(lowlist_item), context);
appendStringInfoChar(buf, ':');
lowlist_item = lnext(lowlist_item);
}
deparseExpr(lfirst(uplist_item), context);
appendStringInfoChar(buf, ']');
}
appendStringInfoChar(buf, ')');
}
/*
* Deparse a function call.
*/
static void
deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
HeapTuple proctup;
Form_pg_proc procform;
const char *proname;
bool use_variadic;
bool first;
ListCell *arg;
/*
* If the function call came from an implicit coercion, then just show the
* first argument.
*/
if (node->funcformat == COERCE_IMPLICIT_CAST)
{
deparseExpr((Expr *) linitial(node->args), context);
return;
}
/*
* If the function call came from a cast, then show the first argument
* plus an explicit cast operation.
*/
if (node->funcformat == COERCE_EXPLICIT_CAST)
{
Oid rettype = node->funcresulttype;
int32 coercedTypmod;
/* Get the typmod if this is a length-coercion function */
(void) exprIsLengthCoercion((Node *) node, &coercedTypmod);
deparseExpr((Expr *) linitial(node->args), context);
appendStringInfo(buf, "::%s",
format_type_with_typemod(rettype, coercedTypmod));
return;
}
/*
* Normal function: display as proname(args).
*/
proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(node->funcid));
if (!HeapTupleIsValid(proctup))
elog(ERROR, "cache lookup failed for function %u", node->funcid);
procform = (Form_pg_proc) GETSTRUCT(proctup);
/* Check if need to print VARIADIC (cf. ruleutils.c) */
use_variadic = node->funcvariadic;
/* Print schema name only if it's not pg_catalog */
if (procform->pronamespace != PG_CATALOG_NAMESPACE)
{
const char *schemaname;
schemaname = get_namespace_name(procform->pronamespace);
appendStringInfo(buf, "%s.", quote_identifier(schemaname));
}
/* Deparse the function name ... */
proname = NameStr(procform->proname);
appendStringInfo(buf, "%s(", quote_identifier(proname));
/* ... and all the arguments */
first = true;
foreach(arg, node->args)
{
if (!first)
appendStringInfoString(buf, ", ");
if (use_variadic && lnext(arg) == NULL)
appendStringInfoString(buf, "VARIADIC ");
deparseExpr((Expr *) lfirst(arg), context);
first = false;
}
appendStringInfoChar(buf, ')');
ReleaseSysCache(proctup);
}
/*
* Deparse given operator expression. To avoid problems around
* priority of operations, we always parenthesize the arguments.
*/
static void
deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
HeapTuple tuple;
Form_pg_operator form;
char oprkind;
ListCell *arg;
/* Retrieve information about the operator from system catalog. */
tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
if (!HeapTupleIsValid(tuple))
elog(ERROR, "cache lookup failed for operator %u", node->opno);
form = (Form_pg_operator) GETSTRUCT(tuple);
oprkind = form->oprkind;
/* Sanity check. */
Assert((oprkind == 'r' && list_length(node->args) == 1) ||
(oprkind == 'l' && list_length(node->args) == 1) ||
(oprkind == 'b' && list_length(node->args) == 2));
/* Always parenthesize the expression. */
appendStringInfoChar(buf, '(');
/* Deparse left operand. */
if (oprkind == 'r' || oprkind == 'b')
{
arg = list_head(node->args);
deparseExpr(lfirst(arg), context);
appendStringInfoChar(buf, ' ');
}
/* Deparse operator name. */
deparseOperatorName(buf, form);
/* Deparse right operand. */
if (oprkind == 'l' || oprkind == 'b')
{
arg = list_tail(node->args);
appendStringInfoChar(buf, ' ');
deparseExpr(lfirst(arg), context);
}
appendStringInfoChar(buf, ')');
ReleaseSysCache(tuple);
}
/*
* Print the name of an operator.
*/
static void
deparseOperatorName(StringInfo buf, Form_pg_operator opform)
{
char *opname;
/* opname is not a SQL identifier, so we should not quote it. */
opname = NameStr(opform->oprname);
/* Print schema name only if it's not pg_catalog */
if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
{
const char *opnspname;
opnspname = get_namespace_name(opform->oprnamespace);
/* Print fully qualified operator name. */
appendStringInfo(buf, "OPERATOR(%s.%s)",
quote_identifier(opnspname), opname);
}
else
{
/* Just print operator name. */
appendStringInfoString(buf, opname);
}
}
/*
* Deparse IS DISTINCT FROM.
*/
static void
deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
Assert(list_length(node->args) == 2);
appendStringInfoChar(buf, '(');
deparseExpr(linitial(node->args), context);
appendStringInfoString(buf, " IS DISTINCT FROM ");
deparseExpr(lsecond(node->args), context);
appendStringInfoChar(buf, ')');
}
/*
* Deparse given ScalarArrayOpExpr expression. To avoid problems
* around priority of operations, we always parenthesize the arguments.
*/
static void
deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
HeapTuple tuple;
Form_pg_operator form;
Expr *arg1;
Expr *arg2;
/* Retrieve information about the operator from system catalog. */
tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
if (!HeapTupleIsValid(tuple))
elog(ERROR, "cache lookup failed for operator %u", node->opno);
form = (Form_pg_operator) GETSTRUCT(tuple);
/* Sanity check. */
Assert(list_length(node->args) == 2);
/* Always parenthesize the expression. */
appendStringInfoChar(buf, '(');
/* Deparse left operand. */
arg1 = linitial(node->args);
deparseExpr(arg1, context);
appendStringInfoChar(buf, ' ');
/* Deparse operator name plus decoration. */
deparseOperatorName(buf, form);
appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");
/* Deparse right operand. */
arg2 = lsecond(node->args);
deparseExpr(arg2, context);
appendStringInfoChar(buf, ')');
/* Always parenthesize the expression. */
appendStringInfoChar(buf, ')');
ReleaseSysCache(tuple);
}
/*
* Deparse a RelabelType (binary-compatible cast) node.
*/
static void
deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
{
deparseExpr(node->arg, context);
if (node->relabelformat != COERCE_IMPLICIT_CAST)
appendStringInfo(context->buf, "::%s",
format_type_with_typemod(node->resulttype,
node->resulttypmod));
}
/*
* Deparse a BoolExpr node.
*/
static void
deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
const char *op = NULL; /* keep compiler quiet */
bool first;
ListCell *lc;
switch (node->boolop)
{
case AND_EXPR:
op = "AND";
break;
case OR_EXPR:
op = "OR";
break;
case NOT_EXPR:
appendStringInfoString(buf, "(NOT ");
deparseExpr(linitial(node->args), context);
appendStringInfoChar(buf, ')');
return;
}
appendStringInfoChar(buf, '(');
first = true;
foreach(lc, node->args)
{
if (!first)
appendStringInfo(buf, " %s ", op);
deparseExpr((Expr *) lfirst(lc), context);
first = false;
}
appendStringInfoChar(buf, ')');
}
/*
* Deparse IS [NOT] NULL expression.
*/
static void
deparseNullTest(NullTest *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
appendStringInfoChar(buf, '(');
deparseExpr(node->arg, context);
if (node->nulltesttype == IS_NULL)
appendStringInfoString(buf, " IS NULL)");
else
appendStringInfoString(buf, " IS NOT NULL)");
}
/*
* Deparse ARRAY[...] construct.
*/
static void
deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
bool first = true;
ListCell *lc;
appendStringInfoString(buf, "ARRAY[");
foreach(lc, node->elements)
{
if (!first)
appendStringInfoString(buf, ", ");
deparseExpr(lfirst(lc), context);
first = false;
}
appendStringInfoChar(buf, ']');
/* If the array is empty, we need an explicit cast to the array type. */
if (node->elements == NIL)
appendStringInfo(buf, "::%s",
format_type_with_typemod(node->array_typeid, -1));
}
/*
* Print the representation of a parameter to be sent to the remote side.
*
* Note: we always label the Param's type explicitly rather than relying on
* transmitting a numeric type OID in PQexecParams(). This allows us to
* avoid assuming that types have the same OIDs on the remote side as they
* do locally --- they need only have the same names.
*/
static void
printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
char *ptypename = format_type_with_typemod(paramtype, paramtypmod);
appendStringInfo(buf, "$%d::%s", paramindex, ptypename);
}
/*
* Print the representation of a placeholder for a parameter that will be
* sent to the remote side at execution time.
*
* This is used when we're just trying to EXPLAIN the remote query.
* We don't have the actual value of the runtime parameter yet, and we don't
* want the remote planner to generate a plan that depends on such a value
* anyway. Thus, we can't do something simple like "$1::paramtype".
* Instead, we emit "((SELECT null::paramtype)::paramtype)".
* In all extant versions of Postgres, the planner will see that as an unknown
* constant value, which is what we want. This might need adjustment if we
* ever make the planner flatten scalar subqueries. Note: the reason for the
* apparently useless outer cast is to ensure that the representation as a
* whole will be parsed as an a_expr and not a select_with_parens; the latter
* would do the wrong thing in the context "x = ANY(...)".
*/
static void
printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
deparse_expr_cxt *context)
{
StringInfo buf = context->buf;
char *ptypename = format_type_with_typemod(paramtype, paramtypmod);
appendStringInfo(buf, "((SELECT null::%s)::%s)", ptypename, ptypename);
}