postgresql/src/backend/parser/parse_expr.c

/*-------------------------------------------------------------------------
 *
 * parse_expr.c
 *	  handle expressions in parser
 *
 * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_expr.c,v 1.127 2002/08/31 22:10:46 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/params.h"
#include "parser/analyze.h"
#include "parser/gramparse.h"
#include "parser/parse.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "parser/parse_func.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "parser/parse_target.h"
#include "parser/parse_type.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


int			max_expr_depth = DEFAULT_MAX_EXPR_DEPTH;
static int	expr_depth_counter = 0;

bool		Transform_null_equals = false;

static Node *parser_typecast_constant(Value *expr, TypeName *typename);
static Node *parser_typecast_expression(ParseState *pstate,
						   Node *expr, TypeName *typename);
static Node *transformColumnRef(ParseState *pstate, ColumnRef *cref);
static Node *transformIndirection(ParseState *pstate, Node *basenode,
					 List *indirection);


/*
 * Initialize for parsing a new query.
 *
 * We reset the expression depth counter here, in case it was left nonzero
 * due to elog()'ing out of the last parsing operation.
 */
void
parse_expr_init(void)
{
	expr_depth_counter = 0;
}


/*
 * transformExpr -
 *	  Analyze and transform expressions. Type checking and type casting is
 *	  done here. The optimizer and the executor cannot handle the original
 *	  (raw) expressions collected by the parse tree. Hence the transformation
 *	  here.
 *
 * NOTE: there are various cases in which this routine will get applied to
 * an already-transformed expression.  Some examples:
 *	1. At least one construct (BETWEEN/AND) puts the same nodes
 *	into two branches of the parse tree; hence, some nodes
 *	are transformed twice.
 *	2. Another way it can happen is that coercion of an operator or
 *	function argument to the required type (via coerce_type())
 *	can apply transformExpr to an already-transformed subexpression.
 *	An example here is "SELECT count(*) + 1.0 FROM table".
 * While it might be possible to eliminate these cases, the path of
 * least resistance so far has been to ensure that transformExpr() does
 * no damage if applied to an already-transformed tree.  This is pretty
 * easy for cases where the transformation replaces one node type with
 * another, such as A_Const => Const; we just do nothing when handed
 * a Const.  More care is needed for node types that are used as both
 * input and output of transformExpr; see SubLink for example.
 */
Node *
transformExpr(ParseState *pstate, Node *expr)
{
	Node	   *result = NULL;

	if (expr == NULL)
		return NULL;

	/*
	 * Guard against an overly complex expression leading to coredump due
	 * to stack overflow here, or in later recursive routines that
	 * traverse expression trees.  Note that this is very unlikely to
	 * happen except with pathological queries; but we don't want someone
	 * to be able to crash the backend quite that easily...
	 */
	if (++expr_depth_counter > max_expr_depth)
		elog(ERROR, "Expression too complex: nesting depth exceeds max_expr_depth = %d",
			 max_expr_depth);

	switch (nodeTag(expr))
	{
		case T_ColumnRef:
			{
				result = transformColumnRef(pstate, (ColumnRef *) expr);
				break;
			}
		case T_ParamRef:
			{
				ParamRef   *pref = (ParamRef *) expr;
				int			paramno = pref->number;
				Oid			paramtyp = param_type(paramno);
				Param	   *param;
				List	   *fields;

				if (!OidIsValid(paramtyp))
					elog(ERROR, "Parameter '$%d' is out of range", paramno);
				param = makeNode(Param);
				param->paramkind = PARAM_NUM;
				param->paramid = (AttrNumber) paramno;
				param->paramname = "<unnamed>";
				param->paramtype = paramtyp;
				result = (Node *) param;
				/* handle qualification, if any */
				foreach(fields, pref->fields)
				{
					result = ParseFuncOrColumn(pstate,
											   makeList1(lfirst(fields)),
											   makeList1(result),
											   false, false, true);
				}
				/* handle subscripts, if any */
				result = transformIndirection(pstate, result,
											  pref->indirection);
				break;
			}
		case T_A_Const:
			{
				A_Const    *con = (A_Const *) expr;
				Value	   *val = &con->val;

				if (con->typename != NULL)
					result = parser_typecast_constant(val, con->typename);
				else
					result = (Node *) make_const(val);
				break;
			}
		case T_ExprFieldSelect:
			{
				ExprFieldSelect *efs = (ExprFieldSelect *) expr;
				List	   *fields;

				result = transformExpr(pstate, efs->arg);
				/* handle qualification, if any */
				foreach(fields, efs->fields)
				{
					result = ParseFuncOrColumn(pstate,
											   makeList1(lfirst(fields)),
											   makeList1(result),
											   false, false, true);
				}
				/* handle subscripts, if any */
				result = transformIndirection(pstate, result,
											  efs->indirection);
				break;
			}
		case T_TypeCast:
			{
				TypeCast   *tc = (TypeCast *) expr;
				Node	   *arg = transformExpr(pstate, tc->arg);

				result = parser_typecast_expression(pstate, arg, tc->typename);
				break;
			}
		case T_A_Expr:
			{
				A_Expr	   *a = (A_Expr *) expr;

				switch (a->oper)
				{
					case OP:
						{
							/*
							 * Special-case "foo = NULL" and "NULL = foo"
							 * for compatibility with standards-broken
							 * products (like Microsoft's).  Turn these
							 * into IS NULL exprs.
							 */
							if (Transform_null_equals &&
								length(a->name) == 1 &&
								strcmp(strVal(lfirst(a->name)), "=") == 0 &&
								(exprIsNullConstant(a->lexpr) ||
								 exprIsNullConstant(a->rexpr)))
							{
								NullTest   *n = makeNode(NullTest);

								n->nulltesttype = IS_NULL;

								if (exprIsNullConstant(a->lexpr))
									n->arg = a->rexpr;
								else
									n->arg = a->lexpr;

								result = transformExpr(pstate,
													   (Node *) n);
							}
							else
							{
								Node	   *lexpr = transformExpr(pstate,
																a->lexpr);
								Node	   *rexpr = transformExpr(pstate,
																a->rexpr);

								result = (Node *) make_op(a->name,
														  lexpr,
														  rexpr);
							}
						}
						break;
					case AND:
						{
							Node	   *lexpr = transformExpr(pstate,
															  a->lexpr);
							Node	   *rexpr = transformExpr(pstate,
															  a->rexpr);
							Expr	   *expr = makeNode(Expr);

							lexpr = coerce_to_boolean(lexpr, "AND");
							rexpr = coerce_to_boolean(rexpr, "AND");

							expr->typeOid = BOOLOID;
							expr->opType = AND_EXPR;
							expr->args = makeList2(lexpr, rexpr);
							result = (Node *) expr;
						}
						break;
					case OR:
						{
							Node	   *lexpr = transformExpr(pstate,
															  a->lexpr);
							Node	   *rexpr = transformExpr(pstate,
															  a->rexpr);
							Expr	   *expr = makeNode(Expr);

							lexpr = coerce_to_boolean(lexpr, "OR");
							rexpr = coerce_to_boolean(rexpr, "OR");

							expr->typeOid = BOOLOID;
							expr->opType = OR_EXPR;
							expr->args = makeList2(lexpr, rexpr);
							result = (Node *) expr;
						}
						break;
					case NOT:
						{
							Node	   *rexpr = transformExpr(pstate,
															  a->rexpr);
							Expr	   *expr = makeNode(Expr);

							rexpr = coerce_to_boolean(rexpr, "NOT");

							expr->typeOid = BOOLOID;
							expr->opType = NOT_EXPR;
							expr->args = makeList1(rexpr);
							result = (Node *) expr;
						}
						break;
					case DISTINCT:
						{
							Node	   *lexpr = transformExpr(pstate,
															  a->lexpr);
							Node	   *rexpr = transformExpr(pstate,
															  a->rexpr);
							result = (Node *) make_op(a->name,
													  lexpr,
													  rexpr);
							((Expr *)result)->opType = DISTINCT_EXPR;
						}
						break;
					case OF:
						{
							List *telem;
							A_Const *n;
							Oid ltype, rtype;
							bool matched = FALSE;

							/* Checking an expression for match to type.
							 * Will result in a boolean constant node.
							 */
							Node	   *lexpr = transformExpr(pstate,
															  a->lexpr);
							ltype = exprType(lexpr);
							foreach(telem, (List *) a->rexpr)
							{
								rtype = LookupTypeName(lfirst(telem));
								matched = (rtype == ltype);
								if (matched) break;
							}

							/* Expect two forms: equals or not equals.
							 * Flip the sense of the result for not equals.
							 */
							if (strcmp(strVal(lfirst(a->name)), "!=") == 0)
								matched = (! matched);

							n = makeNode(A_Const);
							n->val.type = T_String;
							n->val.val.str = (matched? "t": "f");
							n->typename = SystemTypeName("bool");

							result = transformExpr(pstate, (Node *) n);
						}
						break;
				}
				break;
			}
		case T_FuncCall:
			{
				FuncCall   *fn = (FuncCall *) expr;
				List	   *args;

				/* transform the list of arguments */
				foreach(args, fn->args)
					lfirst(args) = transformExpr(pstate,
												 (Node *) lfirst(args));
				result = ParseFuncOrColumn(pstate,
										   fn->funcname,
										   fn->args,
										   fn->agg_star,
										   fn->agg_distinct,
										   false);
				break;
			}
		case T_SubLink:
			{
				SubLink    *sublink = (SubLink *) expr;
				List	   *qtrees;
				Query	   *qtree;

				/* If we already transformed this node, do nothing */
				if (IsA(sublink->subselect, Query))
				{
					result = expr;
					break;
				}
				pstate->p_hasSubLinks = true;
				qtrees = parse_analyze(sublink->subselect, pstate);
				if (length(qtrees) != 1)
					elog(ERROR, "Bad query in subselect");
				qtree = (Query *) lfirst(qtrees);
				if (qtree->commandType != CMD_SELECT ||
					qtree->resultRelation != 0)
					elog(ERROR, "Bad query in subselect");
				sublink->subselect = (Node *) qtree;

				if (sublink->subLinkType == EXISTS_SUBLINK)
				{
					/*
					 * EXISTS needs no lefthand or combining operator.
					 * These fields should be NIL already, but make sure.
					 */
					sublink->lefthand = NIL;
					sublink->oper = NIL;
				}
				else if (sublink->subLinkType == EXPR_SUBLINK)
				{
					List	   *tlist = qtree->targetList;

					/*
					 * Make sure the subselect delivers a single column
					 * (ignoring resjunk targets).
					 */
					if (tlist == NIL ||
						((TargetEntry *) lfirst(tlist))->resdom->resjunk)
						elog(ERROR, "Subselect must have a field");
					while ((tlist = lnext(tlist)) != NIL)
					{
						if (!((TargetEntry *) lfirst(tlist))->resdom->resjunk)
							elog(ERROR, "Subselect must have only one field");
					}

					/*
					 * EXPR needs no lefthand or combining operator. These
					 * fields should be NIL already, but make sure.
					 */
					sublink->lefthand = NIL;
					sublink->oper = NIL;
				}
				else
				{
					/* ALL, ANY, or MULTIEXPR: generate operator list */
					List	   *left_list = sublink->lefthand;
					List	   *right_list = qtree->targetList;
					List	   *op;
					char	   *opname;
					List	   *elist;

					foreach(elist, left_list)
						lfirst(elist) = transformExpr(pstate, lfirst(elist));

					Assert(IsA(sublink->oper, A_Expr));
					op = ((A_Expr *) sublink->oper)->name;
					opname = strVal(llast(op));
					sublink->oper = NIL;

					/* Combining operators other than =/<> is dubious... */
					if (length(left_list) != 1 &&
						strcmp(opname, "=") != 0 && strcmp(opname, "<>") != 0)
						elog(ERROR, "Row comparison cannot use operator %s",
							 opname);

					/*
					 * Scan subquery's targetlist to find values that will
					 * be matched against lefthand values.	We need to
					 * ignore resjunk targets, so doing the outer
					 * iteration over right_list is easier than doing it
					 * over left_list.
					 */
					while (right_list != NIL)
					{
						TargetEntry *tent = (TargetEntry *) lfirst(right_list);
						Node	   *lexpr;
						Operator	optup;
						Form_pg_operator opform;
						Oper	   *newop;

						right_list = lnext(right_list);
						if (tent->resdom->resjunk)
							continue;

						if (left_list == NIL)
							elog(ERROR, "Subselect has too many fields");
						lexpr = lfirst(left_list);
						left_list = lnext(left_list);

						/*
						 * It's OK to use oper() not compatible_oper()
						 * here, because make_subplan() will insert type
						 * coercion calls if needed.
						 */
						optup = oper(op,
									 exprType(lexpr),
									 exprType(tent->expr),
									 false);
						opform = (Form_pg_operator) GETSTRUCT(optup);

						if (opform->oprresult != BOOLOID)
							elog(ERROR, "%s has result type of %s, but must return %s"
								 " to be used with quantified predicate subquery",
								 opname, format_type_be(opform->oprresult),
								 format_type_be(BOOLOID));

						if (get_func_retset(opform->oprcode))
							elog(ERROR, "%s must not return a set"
								 " to be used with quantified predicate subquery",
								 opname);

						newop = makeOper(oprid(optup),	/* opno */
										 InvalidOid,	/* opid */
										 opform->oprresult,
										 false);
						sublink->oper = lappend(sublink->oper, newop);
						ReleaseSysCache(optup);
					}
					if (left_list != NIL)
						elog(ERROR, "Subselect has too few fields");
				}
				result = (Node *) expr;
				break;
			}

		case T_CaseExpr:
			{
				CaseExpr   *c = (CaseExpr *) expr;
				CaseExpr   *newc = makeNode(CaseExpr);
				List	   *newargs = NIL;
				List	   *typeids = NIL;
				List	   *args;
				Node	   *defresult;
				Oid			ptype;

				/* transform the list of arguments */
				foreach(args, c->args)
				{
					CaseWhen   *w = (CaseWhen *) lfirst(args);
					CaseWhen   *neww = makeNode(CaseWhen);
					Node	   *warg;

					Assert(IsA(w, CaseWhen));

					warg = w->expr;
					if (c->arg != NULL)
					{
						/* shorthand form was specified, so expand... */
						warg = (Node *) makeSimpleA_Expr(OP, "=",
														 c->arg, warg);
					}
					neww->expr = transformExpr(pstate, warg);

					neww->expr = coerce_to_boolean(neww->expr, "CASE/WHEN");

					/*
					 * result is NULL for NULLIF() construct - thomas
					 * 1998-11-11
					 */
					warg = w->result;
					if (warg == NULL)
					{
						A_Const    *n = makeNode(A_Const);

						n->val.type = T_Null;
						warg = (Node *) n;
					}
					neww->result = transformExpr(pstate, warg);

					newargs = lappend(newargs, neww);
					typeids = lappendi(typeids, exprType(neww->result));
				}

				newc->args = newargs;

				/*
				 * It's not shorthand anymore, so drop the implicit
				 * argument. This is necessary to keep any re-application
				 * of transformExpr from doing the wrong thing.
				 */
				newc->arg = NULL;

				/* transform the default clause */
				defresult = c->defresult;
				if (defresult == NULL)
				{
					A_Const    *n = makeNode(A_Const);

					n->val.type = T_Null;
					defresult = (Node *) n;
				}
				newc->defresult = transformExpr(pstate, defresult);

				/*
				 * Note: default result is considered the most significant
				 * type in determining preferred type.	This is how the
				 * code worked before, but it seems a little bogus to me
				 * --- tgl
				 */
				typeids = lconsi(exprType(newc->defresult), typeids);

				ptype = select_common_type(typeids, "CASE");
				newc->casetype = ptype;

				/* Convert default result clause, if necessary */
				newc->defresult = coerce_to_common_type(pstate,
														newc->defresult,
														ptype,
														"CASE/ELSE");

				/* Convert when-clause results, if necessary */
				foreach(args, newc->args)
				{
					CaseWhen   *w = (CaseWhen *) lfirst(args);

					w->result = coerce_to_common_type(pstate,
													  w->result,
													  ptype,
													  "CASE/WHEN");
				}

				result = (Node *) newc;
				break;
			}

		case T_NullTest:
			{
				NullTest   *n = (NullTest *) expr;

				n->arg = transformExpr(pstate, n->arg);
				/* the argument can be any type, so don't coerce it */
				result = expr;
				break;
			}

		case T_BooleanTest:
			{
				BooleanTest *b = (BooleanTest *) expr;
				const char *clausename;

				switch (b->booltesttype)
				{
					case IS_TRUE:
						clausename = "IS TRUE";
						break;
					case IS_NOT_TRUE:
						clausename = "IS NOT TRUE";
						break;
					case IS_FALSE:
						clausename = "IS FALSE";
						break;
					case IS_NOT_FALSE:
						clausename = "IS NOT FALSE";
						break;
					case IS_UNKNOWN:
						clausename = "IS UNKNOWN";
						break;
					case IS_NOT_UNKNOWN:
						clausename = "IS NOT UNKNOWN";
						break;
					default:
						elog(ERROR, "transformExpr: unexpected booltesttype %d",
							 (int) b->booltesttype);
						clausename = NULL;	/* keep compiler quiet */
				}

				b->arg = transformExpr(pstate, b->arg);

				b->arg = coerce_to_boolean(b->arg, clausename);

				result = expr;
				break;
			}

		/*********************************************
		 * Quietly accept node types that may be presented when we are
		 * called on an already-transformed tree.
		 *
		 * Do any other node types need to be accepted?  For now we are
		 * taking a conservative approach, and only accepting node
		 * types that are demonstrably necessary to accept.
		 *********************************************/
		case T_Expr:
		case T_Var:
		case T_Const:
		case T_Param:
		case T_Aggref:
		case T_ArrayRef:
		case T_FieldSelect:
		case T_RelabelType:
		case T_ConstraintTest:
			{
				result = (Node *) expr;
				break;
			}

		default:
			/* should not reach here */
			elog(ERROR, "transformExpr: does not know how to transform node %d"
				 " (internal error)", nodeTag(expr));
			break;
	}

	expr_depth_counter--;

	return result;
}

static Node *
transformIndirection(ParseState *pstate, Node *basenode, List *indirection)
{
	if (indirection == NIL)
		return basenode;
	return (Node *) transformArraySubscripts(pstate,
											 basenode, exprType(basenode),
											 indirection, false, NULL);
}

static Node *
transformColumnRef(ParseState *pstate, ColumnRef *cref)
{
	int			numnames = length(cref->fields);
	Node	   *node;
	RangeVar   *rv;

	/*----------
	 * The allowed syntaxes are:
	 *
	 * A		First try to resolve as unqualified column name;
	 *			if no luck, try to resolve as unqual. table name (A.*).
	 * A.B		A is an unqual. table name; B is either a
	 *			column or function name (trying column name first).
	 * A.B.C	schema A, table B, col or func name C.
	 * A.B.C.D	catalog A, schema B, table C, col or func D.
	 * A.*		A is an unqual. table name; means whole-row value.
	 * A.B.*	whole-row value of table B in schema A.
	 * A.B.C.*	whole-row value of table C in schema B in catalog A.
	 *
	 * We do not need to cope with bare "*"; that will only be accepted by
	 * the grammar at the top level of a SELECT list, and transformTargetList
	 * will take care of it before it ever gets here.
	 *
	 * Currently, if a catalog name is given then it must equal the current
	 * database name; we check it here and then discard it.
	 *
	 * For whole-row references, the result is an untransformed RangeVar,
	 * which will work as the argument to a function call, but not in any
	 * other context at present.  (We could instead coerce to a whole-row Var,
	 * but that will fail for subselect and join RTEs, because there is no
	 * pg_type entry for their rowtypes.)
	 *----------
	 */
	switch (numnames)
	{
		case 1:
		{
			char   *name = strVal(lfirst(cref->fields));

			/* Try to identify as an unqualified column */
			node = colnameToVar(pstate, name);

			if (node == NULL)
			{
				/*
				 * Not known as a column of any range-table entry, so
				 * try to find the name as a relation ... but not if
				 * subscripts appear.  Note also that only relations
				 * already entered into the rangetable will be recognized.
				 *
				 * This is a hack for backwards compatibility with PostQUEL-
				 * inspired syntax.  The preferred form now is "rel.*".
				 */
				int		levels_up;

				if (cref->indirection == NIL &&
					refnameRangeTblEntry(pstate, NULL, name,
										 &levels_up) != NULL)
				{
					rv = makeNode(RangeVar);
					rv->relname = name;
					rv->inhOpt = INH_DEFAULT;
					node = (Node *) rv;
				}
				else
					elog(ERROR, "Attribute \"%s\" not found", name);
			}
			break;
		}
		case 2:
		{
			char   *name1 = strVal(lfirst(cref->fields));
			char   *name2 = strVal(lsecond(cref->fields));

			/* Whole-row reference? */
			if (strcmp(name2, "*") == 0)
			{
				rv = makeNode(RangeVar);
				rv->relname = name1;
				rv->inhOpt = INH_DEFAULT;
				node = (Node *) rv;
				break;
			}

			/* Try to identify as a once-qualified column */
			node = qualifiedNameToVar(pstate, NULL, name1, name2, true);
			if (node == NULL)
			{
				/*
				 * Not known as a column of any range-table entry, so
				 * try it as a function call.  Here, we will create an
				 * implicit RTE for tables not already entered.
				 */
				rv = makeNode(RangeVar);
				rv->relname = name1;
				rv->inhOpt = INH_DEFAULT;
				node = ParseFuncOrColumn(pstate,
										 makeList1(makeString(name2)),
										 makeList1(rv),
										 false, false, true);
			}
			break;
		}
		case 3:
		{
			char   *name1 = strVal(lfirst(cref->fields));
			char   *name2 = strVal(lsecond(cref->fields));
			char   *name3 = strVal(lfirst(lnext(lnext(cref->fields))));

			/* Whole-row reference? */
			if (strcmp(name3, "*") == 0)
			{
				rv = makeNode(RangeVar);
				rv->schemaname = name1;
				rv->relname = name2;
				rv->inhOpt = INH_DEFAULT;
				node = (Node *) rv;
				break;
			}

			/* Try to identify as a twice-qualified column */
			node = qualifiedNameToVar(pstate, name1, name2, name3, true);
			if (node == NULL)
			{
				/* Try it as a function call */
				rv = makeNode(RangeVar);
				rv->schemaname = name1;
				rv->relname = name2;
				rv->inhOpt = INH_DEFAULT;
				node = ParseFuncOrColumn(pstate,
										 makeList1(makeString(name3)),
										 makeList1(rv),
										 false, false, true);
			}
			break;
		}
		case 4:
		{
			char   *name1 = strVal(lfirst(cref->fields));
			char   *name2 = strVal(lsecond(cref->fields));
			char   *name3 = strVal(lfirst(lnext(lnext(cref->fields))));
			char   *name4 = strVal(lfirst(lnext(lnext(lnext(cref->fields)))));

			/*
			 * We check the catalog name and then ignore it.
			 */
			if (strcmp(name1, DatabaseName) != 0)
				elog(ERROR, "Cross-database references are not implemented");

			/* Whole-row reference? */
			if (strcmp(name4, "*") == 0)
			{
				rv = makeNode(RangeVar);
				rv->schemaname = name2;
				rv->relname = name3;
				rv->inhOpt = INH_DEFAULT;
				node = (Node *) rv;
				break;
			}

			/* Try to identify as a twice-qualified column */
			node = qualifiedNameToVar(pstate, name2, name3, name4, true);
			if (node == NULL)
			{
				/* Try it as a function call */
				rv = makeNode(RangeVar);
				rv->schemaname = name2;
				rv->relname = name3;
				rv->inhOpt = INH_DEFAULT;
				node = ParseFuncOrColumn(pstate,
										 makeList1(makeString(name4)),
										 makeList1(rv),
										 false, false, true);
			}
			break;
		}
		default:
			elog(ERROR, "Invalid qualified name syntax (too many names)");
			node = NULL;		/* keep compiler quiet */
			break;
	}

	return transformIndirection(pstate, node, cref->indirection);
}

/*
 *	exprType -
 *	  returns the Oid of the type of the expression. (Used for typechecking.)
 */
Oid
exprType(Node *expr)
{
	Oid			type = (Oid) InvalidOid;

	if (!expr)
		return type;

	switch (nodeTag(expr))
	{
		case T_Var:
			type = ((Var *) expr)->vartype;
			break;
		case T_Expr:
			type = ((Expr *) expr)->typeOid;
			break;
		case T_Const:
			type = ((Const *) expr)->consttype;
			break;
		case T_ArrayRef:
			type = ((ArrayRef *) expr)->refrestype;
			break;
		case T_Aggref:
			type = ((Aggref *) expr)->aggtype;
			break;
		case T_Param:
			type = ((Param *) expr)->paramtype;
			break;
		case T_FieldSelect:
			type = ((FieldSelect *) expr)->resulttype;
			break;
		case T_RelabelType:
			type = ((RelabelType *) expr)->resulttype;
			break;
		case T_SubLink:
			{
				SubLink    *sublink = (SubLink *) expr;

				if (sublink->subLinkType == EXPR_SUBLINK)
				{
					/* get the type of the subselect's first target column */
					Query	   *qtree = (Query *) sublink->subselect;
					TargetEntry *tent;

					if (!qtree || !IsA(qtree, Query))
						elog(ERROR, "exprType: Cannot get type for untransformed sublink");
					tent = (TargetEntry *) lfirst(qtree->targetList);
					type = tent->resdom->restype;
				}
				else
				{
					/* for all other sublink types, result is boolean */
					type = BOOLOID;
				}
			}
			break;
		case T_CaseExpr:
			type = ((CaseExpr *) expr)->casetype;
			break;
		case T_CaseWhen:
			type = exprType(((CaseWhen *) expr)->result);
			break;
		case T_NullTest:
			type = BOOLOID;
			break;
		case T_BooleanTest:
			type = BOOLOID;
			break;
		case T_ConstraintTest:
			type = exprType(((ConstraintTest *) expr)->arg);
			break;
		default:
			elog(ERROR, "exprType: Do not know how to get type for %d node",
				 nodeTag(expr));
			break;
	}
	return type;
}

/*
 *	exprTypmod -
 *	  returns the type-specific attrmod of the expression, if it can be
 *	  determined.  In most cases, it can't and we return -1.
 */
int32
exprTypmod(Node *expr)
{
	if (!expr)
		return -1;

	switch (nodeTag(expr))
	{
		case T_Var:
			return ((Var *) expr)->vartypmod;
		case T_Const:
			{
				/* Be smart about string constants... */
				Const	   *con = (Const *) expr;

				switch (con->consttype)
				{
					case BPCHAROID:
						if (!con->constisnull)
							return VARSIZE(DatumGetPointer(con->constvalue));
						break;
					default:
						break;
				}
			}
			break;
		case T_Expr:
			{
				int32		coercedTypmod;

				/* Be smart about length-coercion functions... */
				if (exprIsLengthCoercion(expr, &coercedTypmod))
					return coercedTypmod;
			}
			break;
		case T_FieldSelect:
			return ((FieldSelect *) expr)->resulttypmod;
		case T_RelabelType:
			return ((RelabelType *) expr)->resulttypmod;
		case T_CaseExpr:
			{
				/*
				 * If all the alternatives agree on type/typmod, return
				 * that typmod, else use -1
				 */
				CaseExpr   *cexpr = (CaseExpr *) expr;
				Oid			casetype = cexpr->casetype;
				int32		typmod;
				List	   *arg;

				if (!cexpr->defresult)
					return -1;
				if (exprType(cexpr->defresult) != casetype)
					return -1;
				typmod = exprTypmod(cexpr->defresult);
				if (typmod < 0)
					return -1;	/* no point in trying harder */
				foreach(arg, cexpr->args)
				{
					CaseWhen   *w = (CaseWhen *) lfirst(arg);

					Assert(IsA(w, CaseWhen));
					if (exprType(w->result) != casetype)
						return -1;
					if (exprTypmod(w->result) != typmod)
						return -1;
				}
				return typmod;
			}
			break;
		case T_ConstraintTest:
			return exprTypmod(((ConstraintTest *) expr)->arg);

		default:
			break;
	}
	return -1;
}

/*
 * exprIsLengthCoercion
 *		Detect whether an expression tree is an application of a datatype's
 *		typmod-coercion function.  Optionally extract the result's typmod.
 *
 * If coercedTypmod is not NULL, the typmod is stored there if the expression
 * is a length-coercion function, else -1 is stored there.
 *
 * We assume that a two-argument function named for a datatype, whose
 * output and first argument types are that datatype, and whose second
 * input is an int32 constant, represents a forced length coercion.
 *
 * XXX It'd be better if the parsetree retained some explicit indication
 * of the coercion, so we didn't need these heuristics.
 */
bool
exprIsLengthCoercion(Node *expr, int32 *coercedTypmod)
{
	Func	   *func;
	Const	   *second_arg;
	HeapTuple	procTuple;
	HeapTuple	typeTuple;
	Form_pg_proc procStruct;
	Form_pg_type typeStruct;

	if (coercedTypmod != NULL)
		*coercedTypmod = -1;	/* default result on failure */

	/* Is it a function-call at all? */
	if (expr == NULL ||
		!IsA(expr, Expr) ||
		((Expr *) expr)->opType != FUNC_EXPR)
		return false;
	func = (Func *) (((Expr *) expr)->oper);
	Assert(IsA(func, Func));

	/*
	 * If it's not a two-argument function with the second argument being
	 * an int4 constant, it can't have been created from a length
	 * coercion.
	 */
	if (length(((Expr *) expr)->args) != 2)
		return false;
	second_arg = (Const *) lsecond(((Expr *) expr)->args);
	if (!IsA(second_arg, Const) ||
		second_arg->consttype != INT4OID ||
		second_arg->constisnull)
		return false;

	/*
	 * Lookup the function in pg_proc
	 */
	procTuple = SearchSysCache(PROCOID,
							   ObjectIdGetDatum(func->funcid),
							   0, 0, 0);
	if (!HeapTupleIsValid(procTuple))
		elog(ERROR, "cache lookup for proc %u failed", func->funcid);
	procStruct = (Form_pg_proc) GETSTRUCT(procTuple);

	/*
	 * It must be a function with two arguments where the first is of the
	 * same type as the return value and the second is an int4. Also, just
	 * to be sure, check return type agrees with expr node.
	 */
	if (procStruct->pronargs != 2 ||
		procStruct->prorettype != procStruct->proargtypes[0] ||
		procStruct->proargtypes[1] != INT4OID ||
		procStruct->prorettype != ((Expr *) expr)->typeOid)
	{
		ReleaseSysCache(procTuple);
		return false;
	}

	/*
	 * Furthermore, the name and namespace of the function must be the same
	 * as its result type's name/namespace (cf. find_coercion_function).
	 */
	typeTuple = SearchSysCache(TYPEOID,
							   ObjectIdGetDatum(procStruct->prorettype),
							   0, 0, 0);
	if (!HeapTupleIsValid(typeTuple))
		elog(ERROR, "cache lookup for type %u failed",
			 procStruct->prorettype);
	typeStruct = (Form_pg_type) GETSTRUCT(typeTuple);
	if (strcmp(NameStr(procStruct->proname),
			   NameStr(typeStruct->typname)) != 0 ||
		procStruct->pronamespace != typeStruct->typnamespace)
	{
		ReleaseSysCache(procTuple);
		ReleaseSysCache(typeTuple);
		return false;
	}

	/*
	 * OK, it is indeed a length-coercion function.
	 */
	if (coercedTypmod != NULL)
		*coercedTypmod = DatumGetInt32(second_arg->constvalue);

	ReleaseSysCache(procTuple);
	ReleaseSysCache(typeTuple);
	return true;
}

/*
 * Produce an appropriate Const node from a constant value produced
 * by the parser and an explicit type name to cast to.
 */
static Node *
parser_typecast_constant(Value *expr, TypeName *typename)
{
	Type		tp;
	Datum		datum;
	Const	   *con;
	char	   *const_string = NULL;
	bool		string_palloced = false;
	bool		isNull = false;

	tp = typenameType(typename);

	switch (nodeTag(expr))
	{
		case T_Integer:
			const_string = DatumGetCString(DirectFunctionCall1(int4out,
										 Int32GetDatum(expr->val.ival)));
			string_palloced = true;
			break;
		case T_Float:
		case T_String:
		case T_BitString:
			const_string = expr->val.str;
			break;
		case T_Null:
			isNull = true;
			break;
		default:
			elog(ERROR, "Cannot cast this expression to type '%s'",
				 typeTypeName(tp));
	}

	if (isNull)
		datum = (Datum) NULL;
	else
		datum = stringTypeDatum(tp, const_string, typename->typmod);

	con = makeConst(typeTypeId(tp),
					typeLen(tp),
					datum,
					isNull,
					typeByVal(tp),
					false,		/* not a set */
					true /* is cast */ );

	if (string_palloced)
		pfree(const_string);

	ReleaseSysCache(tp);

	return (Node *) con;
}

/*
 * Handle an explicit CAST applied to a non-constant expression.
 * (Actually, this works for constants too, but gram.y won't generate
 * a TypeCast node if the argument is just a constant.)
 *
 * The given expr has already been transformed, but we need to lookup
 * the type name and then apply any necessary coercion function(s).
 */
static Node *
parser_typecast_expression(ParseState *pstate,
						   Node *expr, TypeName *typename)
{
	Oid			inputType = exprType(expr);
	Oid			targetType;

	targetType = typenameTypeId(typename);

	if (inputType == InvalidOid)
		return expr;			/* do nothing if NULL input */

	if (inputType != targetType)
	{
		expr = CoerceTargetExpr(pstate, expr, inputType,
								targetType, typename->typmod,
								true); /* explicit coercion */
		if (expr == NULL)
			elog(ERROR, "Cannot cast type '%s' to '%s'",
				 format_type_be(inputType),
				 format_type_be(targetType));
	}

	/*
	 * If the target is a fixed-length type, it may need a length coercion
	 * as well as a type coercion.
	 */
	expr = coerce_type_typmod(pstate, expr,
							  targetType, typename->typmod);

	return expr;
}