parse_clause.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

				r_colvar = list_nth(r_colvars, r_index);
				r_usingvars = lappend(r_usingvars, r_colvar);

				res_colnames = lappend(res_colnames, lfirst(ucol));
				res_colvars = lappend(res_colvars,
									  buildMergedJoinVar(pstate,
														 j->jointype,
														 l_colvar,
														 r_colvar));
			}

			j->quals = transformJoinUsingClause(pstate,
												l_usingvars,
												r_usingvars);
		}
		else if (j->quals)
		{
			/* User-written ON-condition; transform it */
			j->quals = transformJoinOnClause(pstate, j,
											 l_rte, r_rte,
											 my_relnamespace,
											 my_containedRels);
		}
		else
		{
			/* CROSS JOIN: no quals */
		}

		/* Add remaining columns from each side to the output columns */
		extractRemainingColumns(res_colnames,
								l_colnames, l_colvars,
								&l_colnames, &l_colvars);
		extractRemainingColumns(res_colnames,
								r_colnames, r_colvars,
								&r_colnames, &r_colvars);
		res_colnames = list_concat(res_colnames, l_colnames);
		res_colvars = list_concat(res_colvars, l_colvars);
		res_colnames = list_concat(res_colnames, r_colnames);
		res_colvars = list_concat(res_colvars, r_colvars);

		/*
		 * Check alias (AS clause), if any.
		 */
		if (j->alias)
		{
			if (j->alias->colnames != NIL)
			{
				if (list_length(j->alias->colnames) > list_length(res_colnames))
					ereport(ERROR,
							(errcode(ERRCODE_SYNTAX_ERROR),
							 errmsg("column alias list for \"%s\" has too many entries",
									j->alias->aliasname)));
			}
		}

		/*
		 * Now build an RTE for the result of the join
		 */
		rte = addRangeTableEntryForJoin(pstate,
										res_colnames,
										j->jointype,
										res_colvars,
										j->alias,
										true);

		/* assume new rte is at end */
		j->rtindex = list_length(pstate->p_rtable);
		Assert(rte == rt_fetch(j->rtindex, pstate->p_rtable));

		*top_rte = rte;
		*top_rti = j->rtindex;

		/*
		 * Prepare returned namespace list.  If the JOIN has an alias then it
		 * hides the contained RTEs as far as the relnamespace goes;
		 * otherwise, put the contained RTEs and *not* the JOIN into
		 * relnamespace.
		 */
		if (j->alias)
		{
			*relnamespace = list_make1(rte);
			list_free(my_relnamespace);
		}
		else
			*relnamespace = my_relnamespace;

		/*
		 * Include join RTE in returned containedRels set
		 */
		*containedRels = bms_add_member(my_containedRels, j->rtindex);

		return (Node *) j;
	}
	else
		elog(ERROR, "unrecognized node type: %d", (int) nodeTag(n));
	return NULL;				/* can't get here, keep compiler quiet */
}

/*
 * buildMergedJoinVar -
 *	  generate a suitable replacement expression for a merged join column
 */
static Node *
buildMergedJoinVar(ParseState *pstate, JoinType jointype,
				   Var *l_colvar, Var *r_colvar)
{
	Oid			outcoltype;
	int32		outcoltypmod;
	Node	   *l_node,
			   *r_node,
			   *res_node;

	/*
	 * Choose output type if input types are dissimilar.
	 */
	outcoltype = l_colvar->vartype;
	outcoltypmod = l_colvar->vartypmod;
	if (outcoltype != r_colvar->vartype)
	{
		outcoltype = select_common_type(list_make2_oid(l_colvar->vartype,
													   r_colvar->vartype),
										"JOIN/USING");
		outcoltypmod = -1;		/* ie, unknown */
	}
	else if (outcoltypmod != r_colvar->vartypmod)
	{
		/* same type, but not same typmod */
		outcoltypmod = -1;		/* ie, unknown */
	}

	/*
	 * Insert coercion functions if needed.  Note that a difference in typmod
	 * can only happen if input has typmod but outcoltypmod is -1. In that
	 * case we insert a RelabelType to clearly mark that result's typmod is
	 * not same as input.  We never need coerce_type_typmod.
	 */
	if (l_colvar->vartype != outcoltype)
		l_node = coerce_type(pstate, (Node *) l_colvar, l_colvar->vartype,
							 outcoltype, outcoltypmod,
							 COERCION_IMPLICIT, COERCE_IMPLICIT_CAST);
	else if (l_colvar->vartypmod != outcoltypmod)
		l_node = (Node *) makeRelabelType((Expr *) l_colvar,
										  outcoltype, outcoltypmod,
										  COERCE_IMPLICIT_CAST);
	else
		l_node = (Node *) l_colvar;

	if (r_colvar->vartype != outcoltype)
		r_node = coerce_type(pstate, (Node *) r_colvar, r_colvar->vartype,
							 outcoltype, outcoltypmod,
							 COERCION_IMPLICIT, COERCE_IMPLICIT_CAST);
	else if (r_colvar->vartypmod != outcoltypmod)
		r_node = (Node *) makeRelabelType((Expr *) r_colvar,
										  outcoltype, outcoltypmod,
										  COERCE_IMPLICIT_CAST);
	else
		r_node = (Node *) r_colvar;

	/*
	 * Choose what to emit
	 */
	switch (jointype)
	{
		case JOIN_INNER:

			/*
			 * We can use either var; prefer non-coerced one if available.
			 */
			if (IsA(l_node, Var))
				res_node = l_node;
			else if (IsA(r_node, Var))
				res_node = r_node;
			else
				res_node = l_node;
			break;
		case JOIN_LEFT:
			/* Always use left var */
			res_node = l_node;
			break;
		case JOIN_RIGHT:
			/* Always use right var */
			res_node = r_node;
			break;
		case JOIN_FULL:
			{
				/*
				 * Here we must build a COALESCE expression to ensure that the
				 * join output is non-null if either input is.
				 */
				CoalesceExpr *c = makeNode(CoalesceExpr);

				c->coalescetype = outcoltype;
				c->args = list_make2(l_node, r_node);
				res_node = (Node *) c;
				break;
			}
		default:
			elog(ERROR, "unrecognized join type: %d", (int) jointype);
			res_node = NULL;	/* keep compiler quiet */
			break;
	}

	return res_node;
}


/*
 * transformWhereClause -
 *	  Transform the qualification and make sure it is of type boolean.
 *	  Used for WHERE and allied clauses.
 *
 * constructName does not affect the semantics, but is used in error messages
 */
Node *
transformWhereClause(ParseState *pstate, Node *clause,
					 const char *constructName)
{
	Node	   *qual;

	if (clause == NULL)
		return NULL;

	qual = transformExpr(pstate, clause);

	qual = coerce_to_boolean(pstate, qual, constructName);

	return qual;
}


/*
 * transformLimitClause -
 *	  Transform the expression and make sure it is of type integer.
 *	  Used for LIMIT and allied clauses.
 *
 * constructName does not affect the semantics, but is used in error messages
 */
Node *
transformLimitClause(ParseState *pstate, Node *clause,
					 const char *constructName)
{
	Node	   *qual;

	if (clause == NULL)
		return NULL;

	qual = transformExpr(pstate, clause);

	qual = coerce_to_integer(pstate, qual, constructName);

	/*
	 * LIMIT can't refer to any vars or aggregates of the current query; we
	 * don't allow subselects either (though that case would at least be
	 * sensible)
	 */
	if (contain_vars_of_level(qual, 0))
	{
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
		/* translator: %s is name of a SQL construct, eg LIMIT */
				 errmsg("argument of %s must not contain variables",
						constructName)));
	}
	if (checkExprHasAggs(qual))
	{
		ereport(ERROR,
				(errcode(ERRCODE_GROUPING_ERROR),
		/* translator: %s is name of a SQL construct, eg LIMIT */
				 errmsg("argument of %s must not contain aggregates",
						constructName)));
	}
	if (contain_subplans(qual))
	{
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
		/* translator: %s is name of a SQL construct, eg LIMIT */
				 errmsg("argument of %s must not contain subqueries",
						constructName)));
	}

	return qual;
}


/*
 *	findTargetlistEntry -
 *	  Returns the targetlist entry matching the given (untransformed) node.
 *	  If no matching entry exists, one is created and appended to the target
 *	  list as a "resjunk" node.
 *
 * node		the ORDER BY, GROUP BY, or DISTINCT ON expression to be matched
 * tlist	the target list (passed by reference so we can append to it)
 * clause	identifies clause type being processed
 */
static TargetEntry *
findTargetlistEntry(ParseState *pstate, Node *node, List **tlist, int clause)
{
	TargetEntry *target_result = NULL;
	ListCell   *tl;
	Node	   *expr;

	/*----------
	 * Handle two special cases as mandated by the SQL92 spec:
	 *
	 * 1. Bare ColumnName (no qualifier or subscripts)
	 *	  For a bare identifier, we search for a matching column name
	 *	  in the existing target list.	Multiple matches are an error
	 *	  unless they refer to identical values; for example,
	 *	  we allow	SELECT a, a FROM table ORDER BY a
	 *	  but not	SELECT a AS b, b FROM table ORDER BY b
	 *	  If no match is found, we fall through and treat the identifier
	 *	  as an expression.
	 *	  For GROUP BY, it is incorrect to match the grouping item against
	 *	  targetlist entries: according to SQL92, an identifier in GROUP BY
	 *	  is a reference to a column name exposed by FROM, not to a target
	 *	  list column.	However, many implementations (including pre-7.0
	 *	  PostgreSQL) accept this anyway.  So for GROUP BY, we look first
	 *	  to see if the identifier matches any FROM column name, and only
	 *	  try for a targetlist name if it doesn't.  This ensures that we
	 *	  adhere to the spec in the case where the name could be both.
	 *	  DISTINCT ON isn't in the standard, so we can do what we like there;
	 *	  we choose to make it work like ORDER BY, on the rather flimsy
	 *	  grounds that ordinary DISTINCT works on targetlist entries.
	 *
	 * 2. IntegerConstant
	 *	  This means to use the n'th item in the existing target list.
	 *	  Note that it would make no sense to order/group/distinct by an
	 *	  actual constant, so this does not create a conflict with our
	 *	  extension to order/group by an expression.
	 *	  GROUP BY column-number is not allowed by SQL92, but since
	 *	  the standard has no other behavior defined for this syntax,
	 *	  we may as well accept this common extension.
	 *
	 * Note that pre-existing resjunk targets must not be used in either case,
	 * since the user didn't write them in his SELECT list.
	 *
	 * If neither special case applies, fall through to treat the item as
	 * an expression.
	 *----------
	 */
	if (IsA(node, ColumnRef) &&
		list_length(((ColumnRef *) node)->fields) == 1)
	{
		char	   *name = strVal(linitial(((ColumnRef *) node)->fields));

		if (clause == GROUP_CLAUSE)
		{
			/*
			 * In GROUP BY, we must prefer a match against a FROM-clause
			 * column to one against the targetlist.  Look to see if there is
			 * a matching column.  If so, fall through to let transformExpr()
			 * do the rest.  NOTE: if name could refer ambiguously to more
			 * than one column name exposed by FROM, colNameToVar will
			 * ereport(ERROR).	That's just what we want here.
			 *
			 * Small tweak for 7.4.3: ignore matches in upper query levels.
			 * This effectively changes the search order for bare names to (1)
			 * local FROM variables, (2) local targetlist aliases, (3) outer
			 * FROM variables, whereas before it was (1) (3) (2). SQL92 and
			 * SQL99 do not allow GROUPing BY an outer reference, so this
			 * breaks no cases that are legal per spec, and it seems a more
			 * self-consistent behavior.
			 */
			if (colNameToVar(pstate, name, true) != NULL)
				name = NULL;
		}

		if (name != NULL)
		{
			foreach(tl, *tlist)
			{
				TargetEntry *tle = (TargetEntry *) lfirst(tl);

				if (!tle->resjunk &&
					strcmp(tle->resname, name) == 0)
				{
					if (target_result != NULL)
					{
						if (!equal(target_result->expr, tle->expr))
							ereport(ERROR,
									(errcode(ERRCODE_AMBIGUOUS_COLUMN),

							/*
							 * translator: first %s is name of a SQL
							 * construct, eg ORDER BY
							 */
									 errmsg("%s \"%s\" is ambiguous",
											clauseText[clause], name)));
					}
					else
						target_result = tle;
					/* Stay in loop to check for ambiguity */
				}
			}
			if (target_result != NULL)
				return target_result;	/* return the first match */
		}
	}
	if (IsA(node, A_Const))
	{
		Value	   *val = &((A_Const *) node)->val;
		int			targetlist_pos = 0;
		int			target_pos;

		if (!IsA(val, Integer))
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
			/* translator: %s is name of a SQL construct, eg ORDER BY */
					 errmsg("non-integer constant in %s",
							clauseText[clause])));
		target_pos = intVal(val);
		foreach(tl, *tlist)
		{
			TargetEntry *tle = (TargetEntry *) lfirst(tl);

			if (!tle->resjunk)
			{
				if (++targetlist_pos == target_pos)
					return tle; /* return the unique match */
			}