parse_clause.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * parse_clause.c
 *	  handle clauses in parser
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.37 1999/05/26 12:55:35 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "postgres.h"
#include "access/heapam.h"
#include "catalog/pg_type.h"
#include "parser/analyze.h"
#include "parser/parse_clause.h"
#include "parser/parse_expr.h"
#include "parser/parse_node.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "parser/parse_target.h"
#include "parser/parse_coerce.h"
#include "nodes/print.h"

#include "parse.h"


#define ORDER_CLAUSE 0
#define GROUP_CLAUSE 1

static char *clauseText[] = {"ORDER", "GROUP"};

static TargetEntry *
			findTargetlistEntry(ParseState *pstate, Node *node, List *tlist, int clause);

static void parseFromClause(ParseState *pstate, List *frmList, Node **qual);

#ifdef ENABLE_OUTER_JOINS
Node	   *transformUsingClause(ParseState *pstate, List *onList, char *lname, char *rname);

#endif

static char	*transformTableEntry(ParseState *pstate, RangeVar *r);


/*
 * makeRangeTable -
 *	  make a range table with the specified relation (optional) and the
 *	  from_clause.
 */
void
makeRangeTable(ParseState *pstate, char *relname, List *frmList, Node **qual)
{
	RangeTblEntry *rte;
	int			sublevels_up;

	parseFromClause(pstate, frmList, qual);

	if (relname == NULL)
		return;

	if ((refnameRangeTablePosn(pstate, relname, &sublevels_up) == 0)
		|| (sublevels_up != 0))
		rte = addRangeTableEntry(pstate, relname, relname, FALSE, FALSE);
	else
		rte = refnameRangeTableEntry(pstate, relname);

	/* This could only happen for multi-action rules */
	if (pstate->p_target_relation != NULL)
		heap_close(pstate->p_target_relation);

	pstate->p_target_rangetblentry = rte;
	pstate->p_target_relation = heap_open(rte->relid);
	/* will close relation later */
}

/*
 * transformWhereClause -
 *	  transforms the qualification and make sure it is of type Boolean
 *
 * Now accept an additional argument, which is a qualification derived
 * from the JOIN/ON or JOIN/USING syntax.
 * - thomas 1998-12-16
 */
Node *
transformWhereClause(ParseState *pstate, Node *a_expr, Node *o_expr)
{
	A_Expr	   *expr;
	Node	   *qual;

	if ((a_expr == NULL) && (o_expr == NULL))
		return NULL;			/* no qualifiers */

	if ((a_expr != NULL) && (o_expr != NULL))
	{
		A_Expr	   *a = makeNode(A_Expr);

		a->oper = AND;
		a->opname = NULL;
		a->lexpr = o_expr;
		a->rexpr = a_expr;
		expr = a;
	}
	else if (o_expr != NULL)
		expr = (A_Expr *) o_expr;
	else
		expr = (A_Expr *) a_expr;

	pstate->p_in_where_clause = true;
	qual = transformExpr(pstate, (Node *) expr, EXPR_COLUMN_FIRST);
	pstate->p_in_where_clause = false;

	if (exprType(qual) != BOOLOID)
	{
		elog(ERROR, "WHERE clause must return type bool, not type %s",
			 typeidTypeName(exprType(qual)));
	}
	return qual;
}

#ifdef NOT_USED
static Attr *
makeAttr(char *relname, char *attname)
{
	Attr	   *a = makeNode(Attr);

	a->relname = relname;
	a->paramNo = NULL;
	a->attrs = lcons(makeString(attname), NIL);
	a->indirection = NULL;

	return a;
}
#endif

#ifdef ENABLE_OUTER_JOINS
/* transformUsingClause()
 * Take an ON or USING clause from a join expression and expand if necessary.
 */
Node *
transformUsingClause(ParseState *pstate, List *onList, char *lname, char *rname)
{
	A_Expr	   *expr = NULL;
	List	   *on;
	Node	   *qual;

	foreach(on, onList)
	{
		qual = lfirst(on);

		/*
		 * Ident node means it is just a column name from a real USING
		 * clause...
		 */
		if (IsA(qual, Ident))
		{
			Ident	   *i = (Ident *) qual;
			Attr	   *lattr = makeAttr(lname, i->name);
			Attr	   *rattr = makeAttr(rname, i->name);
			A_Expr	   *e = makeNode(A_Expr);

			e->oper = OP;
			e->opname = "=";
			e->lexpr = (Node *) lattr;
			e->rexpr = (Node *) rattr;

			if (expr != NULL)
			{
				A_Expr	   *a = makeNode(A_Expr);

				a->oper = AND;
				a->opname = NULL;
				a->lexpr = (Node *) expr;
				a->rexpr = (Node *) e;
				expr = a;
			}
			else
				expr = e;
		}

		/* otherwise, we have an expression from an ON clause... */
		else
		{
			if (expr != NULL)
			{
				A_Expr	   *a = makeNode(A_Expr);

				a->oper = AND;
				a->opname = NULL;
				a->lexpr = (Node *) expr;
				a->rexpr = (Node *) qual;
				expr = a;
			}
			else
				expr = (A_Expr *) qual;
		}
	}
	return ((Node *) transformExpr(pstate, (Node *) expr, EXPR_COLUMN_FIRST));
}

#endif

static char *
transformTableEntry(ParseState *pstate, RangeVar *r)
{
	RelExpr    *baserel = r->relExpr;
	char	   *relname = baserel->relname;
	char	   *refname = r->name;
	RangeTblEntry *rte;

	if (refname == NULL)
		refname = relname;

	/*
	 * marks this entry to indicate it comes from the FROM clause. In SQL,
	 * the target list can only refer to range variables specified in the
	 * from clause but we follow the more powerful POSTQUEL semantics and
	 * automatically generate the range variable if not specified. However
	 * there are times we need to know whether the entries are legitimate.
	 *
	 * eg. select * from foo f where f.x = 1; will generate wrong answer if
	 * we expand * to foo.x.
	 */

	rte = addRangeTableEntry(pstate, relname, refname, baserel->inh, TRUE);

	return refname;
}

/*
 * parseFromClause -
 *	  turns the table references specified in the from-clause into a
 *	  range table. The range table may grow as we transform the expressions
 *	  in the target list. (Note that this happens because in POSTQUEL, we
 *	  allow references to relations not specified in the from-clause. We
 *	  also allow now as an extension.)
 *
 * The FROM clause can now contain JoinExpr nodes, which contain parsing info
 * for inner and outer joins. The USING clause must be expanded into a qualification
 * for an inner join at least, since that is compatible with the old syntax.
 * Not sure yet how to handle outer joins, but it will become clear eventually?
 * - thomas 1998-12-16
 */
static void
parseFromClause(ParseState *pstate, List *frmList, Node **qual)
{
	List	   *fl;

	if (qual != NULL)
		*qual = NULL;

	foreach(fl, frmList)
	{
		Node	   *n = lfirst(fl);

		/*
		 * marks this entry to indicate it comes from the FROM clause. In
		 * SQL, the target list can only refer to range variables
		 * specified in the from clause but we follow the more powerful
		 * POSTQUEL semantics and automatically generate the range
		 * variable if not specified. However there are times we need to
		 * know whether the entries are legitimate.
		 *
		 * eg. select * from foo f where f.x = 1; will generate wrong answer
		 * if we expand * to foo.x.
		 */
		if (IsA(n, RangeVar))
			transformTableEntry(pstate, (RangeVar *) n);
		else if (IsA(n, JoinExpr))
		{
			JoinExpr   *j = (JoinExpr *) n;

#ifdef ENABLE_OUTER_JOINS
			char	   *lname = transformTableEntry(pstate, (RangeVar *) j->larg);

#endif
			char	   *rname;

			if (IsA((Node *) j->rarg, RangeVar))
				rname = transformTableEntry(pstate, (RangeVar *) j->rarg);
			else
				elog(ERROR, "Nested JOINs are not yet supported");

#ifdef ENABLE_OUTER_JOINS
			if (j->jointype == INNER_P)
			{

				/*
				 * This is an inner join, so rip apart the join node and
				 * transform into a traditional FROM list. NATURAL JOIN
				 * and USING clauses both change the shape of the result.
				 * Need to generate a list of result columns to use for
				 * target list expansion and validation. Not doing this
				 * yet though!
				 */
				if (IsA(j->quals, List))
					j->quals = lcons(transformUsingClause(pstate, (List *) j->quals, lname, rname), NIL);

				Assert(qual != NULL);

				if (*qual == NULL)
					*qual = lfirst(j->quals);
				else
					elog(ERROR, "Multiple JOIN/ON clauses not handled (internal error)");

				/*
				 * if we are transforming this node back into a FROM list,
				 * then we will need to replace the node with two nodes.
				 * Will need access to the previous list item to change
				 * the link pointer to reference these new nodes. Try
				 * accumulating and returning a new list. - thomas
				 * 1999-01-08 Not doing this yet though!
				 */

			}
			else if ((j->jointype == LEFT)
					 || (j->jointype == RIGHT)
					 || (j->jointype == FULL))
				elog(ERROR, "OUTER JOIN is not implemented");
			else
				elog(ERROR, "Unrecognized JOIN clause; tag is %d (internal error)",
					 j->jointype);
#else
			elog(ERROR, "JOIN expressions are not yet implemented");
#endif
		}
		else
			elog(ERROR, "parseFromClause: unexpected FROM clause node (internal error)"
				 "\n\t%s", nodeToString(n));
	}
}

/*
 *	findTargetlistEntry -
 *	  returns the Resdom in the target list matching the specified varname
 *	  and range. If none exist one is created.
 *
 *	  Rewritten for ver 6.4 to handle expressions in the GROUP/ORDER BY clauses.
 *	   - [e-mail]	1998-07-31
 *
 */
static TargetEntry *
findTargetlistEntry(ParseState *pstate, Node *node, List *tlist, int clause)
{
	List	   *l;
	int			rtable_pos = 0,
				target_pos = 0,
				targetlist_pos = 0;
	TargetEntry *target_result = NULL;
	Value	   *val = NULL;
	char	   *relname = NULL;
	char	   *name = NULL;
	Node	   *expr = NULL;
	int			relCnt = 0;

	/* Pull out some values before looping thru target list  */
	switch (nodeTag(node))
	{
		case T_Attr:
			relname = ((Attr *) node)->relname;
			val = (Value *) lfirst(((Attr *) node)->attrs);
			name = strVal(val);
			rtable_pos = refnameRangeTablePosn(pstate, relname, NULL);
			relCnt = length(pstate->p_rtable);
			break;

		case T_Ident:
			name = ((Ident *) node)->name;
			relCnt = length(pstate->p_rtable);
			break;

		case T_A_Const:
			val = &((A_Const *) node)->val;

			if (nodeTag(val) != T_Integer)
				elog(ERROR, "Illegal Constant in %s BY", clauseText[clause]);
			target_pos = intVal(val);
			break;

		case T_FuncCall:
		case T_A_Expr:
			expr = transformExpr(pstate, node, EXPR_COLUMN_FIRST);
			break;

		default:
			elog(ERROR, "Illegal %s BY node = %d", clauseText[clause], nodeTag(node));
	}

	/*
	 * Loop through target entries and try to match to node
	 */
	foreach(l, tlist)
	{
		TargetEntry *target = (TargetEntry *) lfirst(l);
		Resdom	   *resnode = target->resdom;
		Var		   *var = (Var *) target->expr;
		char	   *resname = resnode->resname;
		int			test_rtable_pos = var->varno;

		++targetlist_pos;

		switch (nodeTag(node))
		{
			case T_Attr:
				if (strcmp(resname, name) == 0 && rtable_pos == test_rtable_pos)
				{

					/*
					 * Check for only 1 table & ORDER BY -ambiguity does
					 * not matter here
					 */
					if (clause == ORDER_CLAUSE && relCnt == 1)
						return target;