clauses.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

									  fselect->resulttype,
									  fselect->resulttypmod))
				return (Node *) makeVar(((Var *) arg)->varno,
										fselect->fieldnum,
										fselect->resulttype,
										fselect->resulttypmod,
										((Var *) arg)->varlevelsup);
		}
		if (arg && IsA(arg, RowExpr))
		{
			RowExpr    *rowexpr = (RowExpr *) arg;

			if (fselect->fieldnum > 0 &&
				fselect->fieldnum <= list_length(rowexpr->args))
			{
				Node	   *fld = (Node *) list_nth(rowexpr->args,
													fselect->fieldnum - 1);

				if (rowtype_field_matches(rowexpr->row_typeid,
										  fselect->fieldnum,
										  fselect->resulttype,
										  fselect->resulttypmod) &&
					fselect->resulttype == exprType(fld) &&
					fselect->resulttypmod == exprTypmod(fld))
					return fld;
			}
		}
		newfselect = makeNode(FieldSelect);
		newfselect->arg = (Expr *) arg;
		newfselect->fieldnum = fselect->fieldnum;
		newfselect->resulttype = fselect->resulttype;
		newfselect->resulttypmod = fselect->resulttypmod;
		return (Node *) newfselect;
	}

	/*
	 * For any node type not handled above, we recurse using
	 * expression_tree_mutator, which will copy the node unchanged but try to
	 * simplify its arguments (if any) using this routine. For example: we
	 * cannot eliminate an ArrayRef node, but we might be able to simplify
	 * constant expressions in its subscripts.
	 */
	return expression_tree_mutator(node, eval_const_expressions_mutator,
								   (void *) context);
}

/*
 * Subroutine for eval_const_expressions: process arguments of an OR clause
 *
 * This includes flattening of nested ORs as well as recursion to
 * eval_const_expressions to simplify the OR arguments.
 *
 * After simplification, OR arguments are handled as follows:
 *		non constant: keep
 *		FALSE: drop (does not affect result)
 *		TRUE: force result to TRUE
 *		NULL: keep only one
 * We must keep one NULL input because ExecEvalOr returns NULL when no input
 * is TRUE and at least one is NULL.  We don't actually include the NULL
 * here, that's supposed to be done by the caller.
 *
 * The output arguments *haveNull and *forceTrue must be initialized FALSE
 * by the caller.  They will be set TRUE if a null constant or true constant,
 * respectively, is detected anywhere in the argument list.
 */
static List *
simplify_or_arguments(List *args,
					  eval_const_expressions_context *context,
					  bool *haveNull, bool *forceTrue)
{
	List	   *newargs = NIL;
	List	   *unprocessed_args;

	/*
	 * Since the parser considers OR to be a binary operator, long OR lists
	 * become deeply nested expressions.  We must flatten these into long
	 * argument lists of a single OR operator.	To avoid blowing out the stack
	 * with recursion of eval_const_expressions, we resort to some tenseness
	 * here: we keep a list of not-yet-processed inputs, and handle flattening
	 * of nested ORs by prepending to the to-do list instead of recursing.
	 */
	unprocessed_args = list_copy(args);
	while (unprocessed_args)
	{
		Node	   *arg = (Node *) linitial(unprocessed_args);

		unprocessed_args = list_delete_first(unprocessed_args);

		/* flatten nested ORs as per above comment */
		if (or_clause(arg))
		{
			List	   *subargs = list_copy(((BoolExpr *) arg)->args);

			/* overly tense code to avoid leaking unused list header */
			if (!unprocessed_args)
				unprocessed_args = subargs;
			else
			{
				List	   *oldhdr = unprocessed_args;

				unprocessed_args = list_concat(subargs, unprocessed_args);
				pfree(oldhdr);
			}
			continue;
		}

		/* If it's not an OR, simplify it */
		arg = eval_const_expressions_mutator(arg, context);

		/*
		 * It is unlikely but not impossible for simplification of a non-OR
		 * clause to produce an OR.  Recheck, but don't be too tense about it
		 * since it's not a mainstream case. In particular we don't worry
		 * about const-simplifying the input twice.
		 */
		if (or_clause(arg))
		{
			List	   *subargs = list_copy(((BoolExpr *) arg)->args);

			unprocessed_args = list_concat(subargs, unprocessed_args);
			continue;
		}

		/*
		 * OK, we have a const-simplified non-OR argument.	Process it per
		 * comments above.
		 */
		if (IsA(arg, Const))
		{
			Const	   *const_input = (Const *) arg;

			if (const_input->constisnull)
				*haveNull = true;
			else if (DatumGetBool(const_input->constvalue))
			{
				*forceTrue = true;

				/*
				 * Once we detect a TRUE result we can just exit the loop
				 * immediately.  However, if we ever add a notion of
				 * non-removable functions, we'd need to keep scanning.
				 */
				return NIL;
			}
			/* otherwise, we can drop the constant-false input */
			continue;
		}

		/* else emit the simplified arg into the result list */
		newargs = lappend(newargs, arg);
	}

	return newargs;
}

/*
 * Subroutine for eval_const_expressions: process arguments of an AND clause
 *
 * This includes flattening of nested ANDs as well as recursion to
 * eval_const_expressions to simplify the AND arguments.
 *
 * After simplification, AND arguments are handled as follows:
 *		non constant: keep
 *		TRUE: drop (does not affect result)
 *		FALSE: force result to FALSE
 *		NULL: keep only one
 * We must keep one NULL input because ExecEvalAnd returns NULL when no input
 * is FALSE and at least one is NULL.  We don't actually include the NULL
 * here, that's supposed to be done by the caller.
 *
 * The output arguments *haveNull and *forceFalse must be initialized FALSE
 * by the caller.  They will be set TRUE if a null constant or false constant,
 * respectively, is detected anywhere in the argument list.
 */
static List *
simplify_and_arguments(List *args,
					   eval_const_expressions_context *context,
					   bool *haveNull, bool *forceFalse)
{
	List	   *newargs = NIL;
	List	   *unprocessed_args;

	/* See comments in simplify_or_arguments */
	unprocessed_args = list_copy(args);
	while (unprocessed_args)
	{
		Node	   *arg = (Node *) linitial(unprocessed_args);

		unprocessed_args = list_delete_first(unprocessed_args);

		/* flatten nested ANDs as per above comment */
		if (and_clause(arg))
		{
			List	   *subargs = list_copy(((BoolExpr *) arg)->args);

			/* overly tense code to avoid leaking unused list header */
			if (!unprocessed_args)
				unprocessed_args = subargs;
			else
			{
				List	   *oldhdr = unprocessed_args;

				unprocessed_args = list_concat(subargs, unprocessed_args);
				pfree(oldhdr);
			}
			continue;
		}

		/* If it's not an AND, simplify it */
		arg = eval_const_expressions_mutator(arg, context);

		/*
		 * It is unlikely but not impossible for simplification of a non-AND
		 * clause to produce an AND.  Recheck, but don't be too tense about it
		 * since it's not a mainstream case. In particular we don't worry
		 * about const-simplifying the input twice.
		 */
		if (and_clause(arg))
		{
			List	   *subargs = list_copy(((BoolExpr *) arg)->args);

			unprocessed_args = list_concat(subargs, unprocessed_args);
			continue;
		}

		/*
		 * OK, we have a const-simplified non-AND argument.  Process it per
		 * comments above.
		 */
		if (IsA(arg, Const))
		{
			Const	   *const_input = (Const *) arg;

			if (const_input->constisnull)
				*haveNull = true;
			else if (!DatumGetBool(const_input->constvalue))
			{
				*forceFalse = true;

				/*
				 * Once we detect a FALSE result we can just exit the loop
				 * immediately.  However, if we ever add a notion of
				 * non-removable functions, we'd need to keep scanning.
				 */
				return NIL;
			}
			/* otherwise, we can drop the constant-true input */
			continue;
		}

		/* else emit the simplified arg into the result list */
		newargs = lappend(newargs, arg);
	}

	return newargs;
}

/*
 * Subroutine for eval_const_expressions: try to simplify boolean equality
 *
 * Input is the list of simplified arguments to the operator.
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the expression.
 *
 * The idea here is to reduce "x = true" to "x" and "x = false" to "NOT x".
 * This is only marginally useful in itself, but doing it in constant folding
 * ensures that we will recognize the two forms as being equivalent in, for
 * example, partial index matching.
 *
 * We come here only if simplify_function has failed; therefore we cannot
 * see two constant inputs, nor a constant-NULL input.
 */
static Expr *
simplify_boolean_equality(List *args)
{
	Expr	   *leftop;
	Expr	   *rightop;

	Assert(list_length(args) == 2);
	leftop = linitial(args);
	rightop = lsecond(args);
	if (leftop && IsA(leftop, Const))
	{
		Assert(!((Const *) leftop)->constisnull);
		if (DatumGetBool(((Const *) leftop)->constvalue))
			return rightop;		/* true = foo */
		else
			return make_notclause(rightop);		/* false = foo */
	}
	if (rightop && IsA(rightop, Const))
	{
		Assert(!((Const *) rightop)->constisnull);
		if (DatumGetBool(((Const *) rightop)->constvalue))
			return leftop;		/* foo = true */
		else
			return make_notclause(leftop);		/* foo = false */
	}
	return NULL;
}

/*
 * Subroutine for eval_const_expressions: try to simplify a function call
 * (which might originally have been an operator; we don't care)
 *
 * Inputs are the function OID, actual result type OID (which is needed for
 * polymorphic functions), and the pre-simplified argument list;
 * also the context data for eval_const_expressions.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function call.
 */
static Expr *
simplify_function(Oid funcid, Oid result_type, List *args,
				  bool allow_inline,
				  eval_const_expressions_context *context)
{
	HeapTuple	func_tuple;
	Expr	   *newexpr;

	/*
	 * We have two strategies for simplification: either execute the function
	 * to deliver a constant result, or expand in-line the body of the
	 * function definition (which only works for simple SQL-language
	 * functions, but that is a common case).  In either case we need access
	 * to the function's pg_proc tuple, so fetch it just once to use in both
	 * attempts.
	 */
	func_tuple = SearchSysCache(PROCOID,
								ObjectIdGetDatum(funcid),
								0, 0, 0);
	if (!HeapTupleIsValid(func_tuple))
		elog(ERROR, "cache lookup failed for function %u", funcid);

	newexpr = evaluate_function(funcid, result_type, args,
								func_tuple, context);

	if (!newexpr && allow_inline)
		newexpr = inline_function(funcid, result_type, args,
								  func_tuple, context);

	ReleaseSysCache(func_tuple);

	return newexpr;
}

/*
 * evaluate_function: try to pre-evaluate a function call
 *
 * We can do this if the function is strict and has any constant-null inputs
 * (just return a null constant), or if the function is immutable and has all
 * constant inputs (call it and return the result as a Const node).  In
 * estimation mode we are willing to pre-evaluate stable functions too.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function.
 */
static Expr *
evaluate_function(Oid funcid, Oid result_type, List *args,
				  HeapTuple func_tuple,
				  eval_const_expressions_context *context)
{
	Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
	bool		has_nonconst_input = false;
	bool		has_null_input = false;
	ListCell   *arg;
	FuncExpr   *newexpr;

	/*
	 * Can't simplify if it returns a set.
	 */
	if (funcform->proretset)
		return NULL;

	/*
	 * Can't simplify if it returns RECORD.  The immediate problem is that it
	 * will be needing an expected tupdesc which we can't supply here.
	 *
	 * In the case where it has OUT parameters, it could get by without an
	 * expected tupdesc, but we still have issues: get_expr_result_type()
	 * doesn't know how to extract type info from a RECORD constant, and in
	 * the case of a NULL function result there doesn't seem to be any clean
	 * way to fix that.  In view of the likelihood of there being still other
	 * gotchas, seems best to leave the function call unreduced.
	 */
	if (funcform->prorettype == RECORDOID)
		return NULL;

	/*
	 * Check for constant inputs and especially constant-NULL inputs.
	 */
	foreach(arg, args)
	{
		if (IsA(lfirst(arg), Const))
			has_null_input |= ((Const *) lfirst(arg))->constisnull;
		else
			has_nonconst_input = true;
	}

	/*
	 * If the function is strict and has a constant-NULL input, it will never
	 * be called at all, so we can replace the call by a NULL constant, even
	 * if there are other inputs that aren't constant, and even if the
	 * function is not otherwise immutable.
	 */
	if (funcform->proisstrict && has_null_input)
		return (Expr *) makeNullConst(result_type);

	/*
	 * Otherwise, can simplify only if all inputs are constants. (For a
	 * non-strict function, constant NULL inputs are treated the same as
	 * constant non-NULL inputs.)
	 */
	if (has_nonconst_input)
		return NULL;

	/*
	 * Ordinarily we are only allowed to simplify immutable functions. But for
	 * purposes of estimation, we consider it okay to simplify functions that
	 * are merely stable; the risk that the result might change from planning
	 * time to execution time is worth taking in preference to not being able
	 * to estimate the value at all.
	 */
	if (funcform->provolatile == PROVOLATILE_IMMUTABLE)
		 /* okay */ ;
	else if (context->estimate && funcform->provolatile == PROVOLATILE_STABLE)
		 /* okay */ ;
	else
		return NULL;

	/*
	 * OK, looks like we can simplify this operator/function.
	 *
	 * Build a new FuncExpr node containing the already-simplified arguments.
	 */
	newexpr = makeNode(FuncExpr);
	newexpr->funcid = funcid;
	newexpr->funcresulttype = result_type;
	newexpr->funcretset = false;
	newexpr->funcformat = COERCE_DONTCARE;		/* doesn't matter */
	newexpr->args = args;

	return evaluate_expr((Expr *) newexpr, result_type);
}

/*
 * inline_function: try to expand a function call inline
 *
 * If the function is a sufficiently simple SQL-language function
 * (just "SELECT expression"), then we can inline it and avoid the rather
 * high per-call overhead of SQL functions.  Furthermore, this can expose
 * opportunities for constant-folding within the function expression.
 *
 * We have to beware of some speci