parse_target.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

				 errmsg("SELECT * with no tables specified is not valid")));

	foreach(l, pstate->p_varnamespace)
	{
		RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
		int			rtindex = RTERangeTablePosn(pstate, rte, NULL);

		target = list_concat(target,
							 expandRelAttrs(pstate, rte, rtindex, 0));
	}

	return target;
}

/*
 * ExpandIndirectionStar()
 *		Turns foo.* (in the target list) into a list of targetlist entries.
 *
 * This handles the case where '*' appears as the last item in A_Indirection.
 */
static List *
ExpandIndirectionStar(ParseState *pstate, A_Indirection *ind)
{
	Node	   *expr;
	TupleDesc	tupleDesc;
	int			numAttrs;
	int			i;
	List	   *te_list = NIL;

	/* Strip off the '*' to create a reference to the rowtype object */
	ind = copyObject(ind);
	ind->indirection = list_truncate(ind->indirection,
									 list_length(ind->indirection) - 1);

	/* And transform that */
	expr = transformExpr(pstate, (Node *) ind);

	/*
	 * Verify it's a composite type, and get the tupdesc.  We use
	 * get_expr_result_type() because that can handle references to functions
	 * returning anonymous record types.  If that fails, use
	 * lookup_rowtype_tupdesc(), which will almost certainly fail as well, but
	 * it will give an appropriate error message.
	 *
	 * If it's a Var of type RECORD, we have to work even harder: we have to
	 * find what the Var refers to, and pass that to get_expr_result_type.
	 * That task is handled by expandRecordVariable().
	 */
	if (IsA(expr, Var) &&
		((Var *) expr)->vartype == RECORDOID)
		tupleDesc = expandRecordVariable(pstate, (Var *) expr, 0);
	else if (get_expr_result_type(expr, NULL, &tupleDesc) != TYPEFUNC_COMPOSITE)
		tupleDesc = CreateTupleDescCopy(lookup_rowtype_tupdesc(exprType(expr),
															   exprTypmod(expr)));
	Assert(tupleDesc);

	/* Generate a list of references to the individual fields */
	numAttrs = tupleDesc->natts;
	for (i = 0; i < numAttrs; i++)
	{
		Form_pg_attribute att = tupleDesc->attrs[i];
		Node	   *fieldnode;
		TargetEntry *te;

		if (att->attisdropped)
			continue;

		/*
		 * If we got a whole-row Var from the rowtype reference, we can expand
		 * the fields as simple Vars.  Otherwise we must generate multiple
		 * copies of the rowtype reference and do FieldSelects.
		 */
		if (IsA(expr, Var) &&
			((Var *) expr)->varattno == InvalidAttrNumber)
		{
			Var		   *var = (Var *) expr;

			fieldnode = (Node *) makeVar(var->varno,
										 i + 1,
										 att->atttypid,
										 att->atttypmod,
										 var->varlevelsup);
		}
		else
		{
			FieldSelect *fselect = makeNode(FieldSelect);

			fselect->arg = (Expr *) copyObject(expr);
			fselect->fieldnum = i + 1;
			fselect->resulttype = att->atttypid;
			fselect->resulttypmod = att->atttypmod;

			fieldnode = (Node *) fselect;
		}

		te = makeTargetEntry((Expr *) fieldnode,
							 (AttrNumber) pstate->p_next_resno++,
							 pstrdup(NameStr(att->attname)),
							 false);
		te_list = lappend(te_list, te);
	}

	return te_list;
}

/*
 * expandRecordVariable
 *		Get the tuple descriptor for a Var of type RECORD, if possible.
 *
 * Since no actual table or view column is allowed to have type RECORD, such
 * a Var must refer to a JOIN or FUNCTION RTE or to a subquery output.	We
 * drill down to find the ultimate defining expression and attempt to infer
 * the tupdesc from it.  We ereport if we can't determine the tupdesc.
 *
 * levelsup is an extra offset to interpret the Var's varlevelsup correctly.
 */
TupleDesc
expandRecordVariable(ParseState *pstate, Var *var, int levelsup)
{
	TupleDesc	tupleDesc;
	int			netlevelsup;
	RangeTblEntry *rte;
	AttrNumber	attnum;
	Node	   *expr;

	/* Check my caller didn't mess up */
	Assert(IsA(var, Var));
	Assert(var->vartype == RECORDOID);

	netlevelsup = var->varlevelsup + levelsup;
	rte = GetRTEByRangeTablePosn(pstate, var->varno, netlevelsup);
	attnum = var->varattno;

	if (attnum == InvalidAttrNumber)
	{
		/* Whole-row reference to an RTE, so expand the known fields */
		List	   *names,
				   *vars;
		ListCell   *lname,
				   *lvar;
		int			i;

		expandRTE(rte, var->varno, 0, false,
				  &names, &vars);

		tupleDesc = CreateTemplateTupleDesc(list_length(vars), false);
		i = 1;
		forboth(lname, names, lvar, vars)
		{
			char	   *label = strVal(lfirst(lname));
			Node	   *varnode = (Node *) lfirst(lvar);

			TupleDescInitEntry(tupleDesc, i,
							   label,
							   exprType(varnode),
							   exprTypmod(varnode),
							   0);
			i++;
		}
		Assert(lname == NULL && lvar == NULL);	/* lists same length? */

		return tupleDesc;
	}

	expr = (Node *) var;		/* default if we can't drill down */

	switch (rte->rtekind)
	{
		case RTE_RELATION:
		case RTE_SPECIAL:

			/*
			 * This case should not occur: a column of a table shouldn't have
			 * type RECORD.  Fall through and fail (most likely) at the
			 * bottom.
			 */
			break;
		case RTE_SUBQUERY:
			{
				/* Subselect-in-FROM: examine sub-select's output expr */
				TargetEntry *ste = get_tle_by_resno(rte->subquery->targetList,
													attnum);

				if (ste == NULL || ste->resjunk)
					elog(ERROR, "subquery %s does not have attribute %d",
						 rte->eref->aliasname, attnum);
				expr = (Node *) ste->expr;
				if (IsA(expr, Var))
				{
					/*
					 * Recurse into the sub-select to see what its Var refers
					 * to.	We have to build an additional level of ParseState
					 * to keep in step with varlevelsup in the subselect.
					 */
					ParseState	mypstate;

					MemSet(&mypstate, 0, sizeof(mypstate));
					mypstate.parentParseState = pstate;
					mypstate.p_rtable = rte->subquery->rtable;
					/* don't bother filling the rest of the fake pstate */

					return expandRecordVariable(&mypstate, (Var *) expr, 0);
				}
				/* else fall through to inspect the expression */
			}
			break;
		case RTE_JOIN:
			/* Join RTE --- recursively inspect the alias variable */
			Assert(attnum > 0 && attnum <= list_length(rte->joinaliasvars));
			expr = (Node *) list_nth(rte->joinaliasvars, attnum - 1);
			if (IsA(expr, Var))
				return expandRecordVariable(pstate, (Var *) expr, netlevelsup);
			/* else fall through to inspect the expression */
			break;
		case RTE_FUNCTION:

			/*
			 * We couldn't get here unless a function is declared with one of
			 * its result columns as RECORD, which is not allowed.
			 */
			break;
	}

	/*
	 * We now have an expression we can't expand any more, so see if
	 * get_expr_result_type() can do anything with it.	If not, pass to
	 * lookup_rowtype_tupdesc() which will probably fail, but will give an
	 * appropriate error message while failing.
	 */
	if (get_expr_result_type(expr, NULL, &tupleDesc) != TYPEFUNC_COMPOSITE)
		tupleDesc = CreateTupleDescCopy(lookup_rowtype_tupdesc(exprType(expr),
															   exprTypmod(expr)));

	return tupleDesc;
}


/*
 * FigureColname -
 *	  if the name of the resulting column is not specified in the target
 *	  list, we have to guess a suitable name.  The SQL spec provides some
 *	  guidance, but not much...
 *
 * Note that the argument is the *untransformed* parse tree for the target
 * item.  This is a shade easier to work with than the transformed tree.
 */
char *
FigureColname(Node *node)
{
	char	   *name = NULL;

	FigureColnameInternal(node, &name);
	if (name != NULL)
		return name;
	/* default result if we can't guess anything */
	return "?column?";
}

static int
FigureColnameInternal(Node *node, char **name)
{
	int			strength = 0;

	if (node == NULL)
		return strength;

	switch (nodeTag(node))
	{
		case T_ColumnRef:
			{
				char	   *fname = NULL;
				ListCell   *l;

				/* find last field name, if any, ignoring "*" */
				foreach(l, ((ColumnRef *) node)->fields)
				{
					Node	   *i = lfirst(l);

					if (strcmp(strVal(i), "*") != 0)
						fname = strVal(i);
				}
				if (fname)
				{
					*name = fname;
					return 2;
				}
			}
			break;
		case T_A_Indirection:
			{
				A_Indirection *ind = (A_Indirection *) node;
				char	   *fname = NULL;
				ListCell   *l;

				/* find last field name, if any, ignoring "*" */
				foreach(l, ind->indirection)
				{
					Node	   *i = lfirst(l);

					if (IsA(i, String) &&
						strcmp(strVal(i), "*") != 0)
						fname = strVal(i);
				}
				if (fname)
				{
					*name = fname;
					return 2;
				}
				return FigureColnameInternal(ind->arg, name);
			}
			break;
		case T_FuncCall:
			*name = strVal(llast(((FuncCall *) node)->funcname));
			return 2;
		case T_A_Expr:
			/* make nullif() act like a regular function */
			if (((A_Expr *) node)->kind == AEXPR_NULLIF)
			{
				*name = "nullif";
				return 2;
			}
			break;
		case T_A_Const:
			if (((A_Const *) node)->typename != NULL)
			{
				*name = strVal(llast(((A_Const *) node)->typename->names));
				return 1;
			}
			break;
		case T_TypeCast:
			strength = FigureColnameInternal(((TypeCast *) node)->arg,
											 name);
			if (strength <= 1)
			{
				if (((TypeCast *) node)->typename != NULL)
				{
					*name = strVal(llast(((TypeCast *) node)->typename->names));
					return 1;
				}
			}
			break;
		case T_CaseExpr:
			strength = FigureColnameInternal((Node *) ((CaseExpr *) node)->defresult,
											 name);
			if (strength <= 1)
			{
				*name = "case";
				return 1;
			}
			break;
		case T_ArrayExpr:
			/* make ARRAY[] act like a function */
			*name = "array";
			return 2;
		case T_RowExpr:
			/* make ROW() act like a function */
			*name = "row";
			return 2;
		case T_CoalesceExpr:
			/* make coalesce() act like a regular function */
			*name = "coalesce";
			return 2;
		case T_MinMaxExpr:
			/* make greatest/least act like a regular function */
			switch (((MinMaxExpr *) node)->op)
			{
				case IS_GREATEST:
					*name = "greatest";
					return 2;
				case IS_LEAST:
					*name = "least";
					return 2;
			}
			break;
		default:
			break;
	}

	return strength;
}