join_nested.result, join_nested.test:

  Added a test case for bug #4922.
sql_select.cc:
  Blocked an optimization performed by join_read_const_table when
  applied to an inner table of a nested outer join.
  It was done to fix bug #4922.
sql_yacc.yy:
  Fixed a typo bug in the rule for join_table.

mysql-test/r/join_nested.result

@@ -1184,3 +1184,27 @@ a	b	a1	b
 4	2	2	2
 5	3	NULL	NULL
 DROP TABLE t0,t1,t2,t3,t4,t5,t6,t7,t8,t9;
+CREATE TABLE t1 (a int);
+CREATE TABLE t2 (a int);
+CREATE TABLE t3 (a int);
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (2);
+INSERT INTO t3 VALUES (2);
+INSERT INTO t1 VALUES (2);
+SELECT * FROM t1 LEFT JOIN (t2 LEFT JOIN t3 ON t2.a=t3.a) ON t1.a=t3.a;
+a	a	a
+1	NULL	NULL
+2	2	2
+SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON t2.a=t3.a ON t1.a=t3.a;
+a	a	a
+1	NULL	NULL
+2	2	2
+DELETE FROM t1 WHERE a=2;
+SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON t2.a=t3.a ON t1.a=t3.a;
+a	a	a
+1	NULL	NULL
+DELETE FROM t2;
+SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON t2.a=t3.a ON t1.a=t3.a;
+a	a	a
+1	NULL	NULL
+DROP TABLE t1,t2,t3;

mysql-test/t/join_nested.test

@@ -700,3 +700,30 @@ SELECT t2.a,t2.b,t3.a1,t3.b
     WHERE t2.a = 4 OR (t2.a > 4 AND t3.a1 IS NULL);
 
 DROP TABLE t0,t1,t2,t3,t4,t5,t6,t7,t8,t9;
+
+CREATE TABLE t1 (a int);
+CREATE TABLE t2 (a int);
+CREATE TABLE t3 (a int);
+
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (2);
+INSERT INTO t3 VALUES (2);
+INSERT INTO t1 VALUES (2);
+
+#check proper syntax for nested outer joins
+
+SELECT * FROM t1 LEFT JOIN (t2 LEFT JOIN t3 ON t2.a=t3.a) ON t1.a=t3.a;
+
+#must be equivalent to:
+
+SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON t2.a=t3.a ON t1.a=t3.a;
+
+#check that everything is al right when all tables contain not more than 1 row
+#(bug #4922)
+
+DELETE FROM t1 WHERE a=2;
+SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON t2.a=t3.a ON t1.a=t3.a;
+DELETE FROM t2;
+SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON t2.a=t3.a ON t1.a=t3.a;
+
+DROP TABLE t1,t2,t3;

sql/sql_select.cc

@@ -1860,7 +1860,8 @@ make_join_statistics(JOIN *join,TABLE_LIST *tables,COND *conds,
 	if (s->dependent & ~(found_const_table_map))
 	  continue;
 	if (table->file->records <= 1L &&
-	    !(table->file->table_flags() & HA_NOT_EXACT_COUNT))
+	    !(table->file->table_flags() & HA_NOT_EXACT_COUNT) &&
+            !table->pos_in_table_list->embedding)
 	{					// system table
 	  int tmp= 0;
 	  s->type=JT_SYSTEM;

sql/sql_yacc.yy

@@ -4593,7 +4593,7 @@ join_table:
 	  '(' using_list ')'
 	  { add_join_on($3,$7); $$=$3; }
 
-	| table_ref LEFT opt_outer JOIN_SYM table_factor ON expr
+	| table_ref LEFT opt_outer JOIN_SYM table_ref ON expr
 	  { add_join_on($5,$7); $5->outer_join|=JOIN_TYPE_LEFT; $$=$5; }
 	| table_ref LEFT opt_outer JOIN_SYM table_factor
 	  {
@@ -4608,7 +4608,7 @@ join_table:
 	    $6->outer_join|=JOIN_TYPE_LEFT;
 	    $$=$6;
 	  }
-	| table_ref RIGHT opt_outer JOIN_SYM table_factor ON expr
+	| table_ref RIGHT opt_outer JOIN_SYM table_ref ON expr
           { 
 	    LEX *lex= Lex;
             if (!($$= lex->current_select->convert_right_join()))