A fix for Bug#11901 "mysql_stmt_attr_set CURSOR_TYPE_READ_ONLY join in

subqry order by server crash": failing DBUG_ASSERT(curr_join == this)
when opening a cursor.
Ensure that for top-level join curr_join == join (always), 
and thus fix the failing assert.
curr_join is a hack to ensure that uncacheable subqueries can be
re-evaluated safely, and should be never different from main join
in case of top-level join.


sql/sql_select.cc:
  - utilize tmp_join only if we evaluate an uncacheable subquery.
sql/sql_select.h:
  - implement JOIN::is_top_level_join()
tests/mysql_client_test.c:
  A test case for Bug#11901 "mysql_stmt_attr_set CURSOR_TYPE_READ_ONLY
   join in subqry order by server crash"

sql/sql_select.cc

@@ -1091,8 +1091,9 @@ JOIN::optimize()
       }
     }
 
-    if (thd->lex->subqueries)
+    if (select_lex->uncacheable && !is_top_level_join())
     {
+      /* If this join belongs to an uncacheable subquery */
       if (!(tmp_join= (JOIN*)thd->alloc(sizeof(JOIN))))
 	DBUG_RETURN(-1);
       error= 0;				// Ensure that tmp_join.error= 0
@@ -1636,9 +1637,7 @@ JOIN::exec()
   curr_join->fields= curr_fields_list;
   curr_join->procedure= procedure;
 
-  if (unit == &thd->lex->unit &&
-      (unit->fake_select_lex == 0 || select_lex == unit->fake_select_lex) &&
-      thd->cursor && tables != const_tables)
+  if (is_top_level_join() && thd->cursor && tables != const_tables)
   {
     /*
       We are here if this is JOIN::exec for the last select of the main unit

sql/sql_select.h

@@ -366,6 +366,11 @@ class JOIN :public Sql_alloc
 	    !group_list);
   }
   bool change_result(select_result *result);
+  bool is_top_level_join() const
+  {
+    return (unit == &thd->lex->unit && (unit->fake_select_lex == 0 ||
+                                        select_lex == unit->fake_select_lex));
+  }
 };
 
 

tests/mysql_client_test.c

@@ -14051,6 +14051,128 @@ static void test_bug11909()
   myquery(rc);
 }
 
+/* Cursors: opening a cursor to a compilicated query with ORDER BY */
+
+static void test_bug11901()
+{
+  MYSQL_STMT *stmt;
+  MYSQL_BIND bind[2];
+  int rc;
+  char workdept[20];
+  ulong workdept_len;
+  uint32 empno;
+  const char *stmt_text;
+
+  myheader("test_bug11901");
+
+  stmt_text= "drop table if exists t1, t2";
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+
+  stmt_text= "create table t1 ("
+    "  empno int(11) not null, firstname varchar(20) not null,"
+    "  midinit varchar(20) not null, lastname varchar(20) not null,"
+    "  workdept varchar(6) not null, salary double not null,"
+    "  bonus float not null, primary key (empno), "
+    " unique key (workdept, empno) "
+    ") default charset=latin1 collate=latin1_bin";
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+
+  stmt_text= "insert into t1 values "
+     "(10,  'CHRISTINE', 'I', 'HAAS',      'A00', 52750, 1000),"
+     "(20,  'MICHAEL',   'L', 'THOMPSON',  'B01', 41250, 800), "
+     "(30,  'SALLY',     'A', 'KWAN',      'C01', 38250, 800), "
+     "(50,  'JOHN',      'B', 'GEYER',     'E01', 40175, 800), "
+     "(60,  'IRVING',    'F', 'STERN',     'D11', 32250, 500), "
+     "(70,  'EVA',       'D', 'PULASKI',   'D21', 36170, 700), "
+     "(90,  'EILEEN',    'W', 'HENDERSON', 'E11', 29750, 600), "
+     "(100, 'THEODORE',  'Q', 'SPENSER',   'E21', 26150, 500), "
+     "(110, 'VINCENZO',  'G', 'LUCCHESSI', 'A00', 46500, 900), "
+     "(120, 'SEAN',      '',  'O\\'CONNELL', 'A00', 29250, 600), "
+     "(130, 'DOLORES',   'M', 'QUINTANA',  'C01', 23800, 500), "
+     "(140, 'HEATHER',   'A', 'NICHOLLS',  'C01', 28420, 600), "
+     "(150, 'BRUCE',     '',  'ADAMSON',   'D11', 25280, 500), "
+     "(160, 'ELIZABETH', 'R', 'PIANKA',    'D11', 22250, 400), "
+     "(170, 'MASATOSHI', 'J', 'YOSHIMURA', 'D11', 24680, 500), "
+     "(180, 'MARILYN',   'S', 'SCOUTTEN',  'D11', 21340, 500), "
+     "(190, 'JAMES',     'H', 'WALKER',    'D11', 20450, 400), "
+     "(200, 'DAVID',     '',  'BROWN',     'D11', 27740, 600), "
+     "(210, 'WILLIAM',   'T', 'JONES',     'D11', 18270, 400), "
+     "(220, 'JENNIFER',  'K', 'LUTZ',      'D11', 29840, 600), "
+     "(230, 'JAMES',     'J', 'JEFFERSON', 'D21', 22180, 400), "
+     "(240, 'SALVATORE', 'M', 'MARINO',    'D21', 28760, 600), "
+     "(250, 'DANIEL',    'S', 'SMITH',     'D21', 19180, 400), "
+     "(260, 'SYBIL',     'P', 'JOHNSON',   'D21', 17250, 300), "
+     "(270, 'MARIA',     'L', 'PEREZ',     'D21', 27380, 500), "
+     "(280, 'ETHEL',     'R', 'SCHNEIDER', 'E11', 26250, 500), "
+     "(290, 'JOHN',      'R', 'PARKER',    'E11', 15340, 300), "
+     "(300, 'PHILIP',    'X', 'SMITH',     'E11', 17750, 400), "
+     "(310, 'MAUDE',     'F', 'SETRIGHT',  'E11', 15900, 300), "
+     "(320, 'RAMLAL',    'V', 'MEHTA',     'E21', 19950, 400), "
+     "(330, 'WING',      '',  'LEE',       'E21', 25370, 500), "
+     "(340, 'JASON',     'R', 'GOUNOT',    'E21', 23840, 500)";
+
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+
+  stmt_text= "create table t2 ("
+    " deptno varchar(6) not null, deptname varchar(20) not null,"
+    " mgrno int(11) not null, location varchar(20) not null,"
+    " admrdept varchar(6) not null, refcntd int(11) not null,"
+    " refcntu int(11) not null, primary key (deptno)"
+    ") default charset=latin1 collate=latin1_bin";
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+
+  stmt_text= "insert into t2 values "
+    "('A00', 'SPIFFY COMPUTER SERV', 10, '', 'A00', 0, 0), "
+    "('B01', 'PLANNING',             20, '', 'A00', 0, 0), "
+    "('C01', 'INFORMATION CENTER',   30, '', 'A00', 0, 0), "
+    "('D01', 'DEVELOPMENT CENTER',   0,  '', 'A00', 0, 0),"
+    "('D11', 'MANUFACTURING SYSTEM', 60, '', 'D01', 0, 0), "
+    "('D21', 'ADMINISTRATION SYSTE', 70, '', 'D01', 0, 0), "
+    "('E01', 'SUPPORT SERVICES',     50, '', 'A00', 0, 0), "
+    "('E11', 'OPERATIONS',           90, '', 'E01', 0, 0), "
+    "('E21', 'SOFTWARE SUPPORT',     100,'', 'E01', 0, 0)";
+  rc= mysql_real_query(mysql, stmt_text, strlen(stmt_text));
+  myquery(rc);
+
+  /* ****** Begin of trace ****** */
+
+  stmt= open_cursor("select t1.empno, t1.workdept "
+                    "from (t1 left join t2 on t2.deptno = t1.workdept) "
+                    "where t2.deptno in "
+                    "   (select t2.deptno "
+                    "    from (t1 left join t2 on t2.deptno = t1.workdept) "
+                    "    where t1.empno = ?) "
+                    "order by 1");
+  bzero(bind, sizeof(bind));
+
+  bind[0].buffer_type= MYSQL_TYPE_LONG;
+  bind[0].buffer= &empno;
+  rc= mysql_stmt_bind_param(stmt, bind);
+  check_execute(stmt, rc);
+
+  bind[1].buffer_type= MYSQL_TYPE_VAR_STRING;
+  bind[1].buffer= (void*) workdept;
+  bind[1].buffer_length= sizeof(workdept);
+  bind[1].length= &workdept_len;
+
+  rc= mysql_stmt_bind_result(stmt, bind);
+  check_execute(stmt, rc);
+
+  empno= 10;
+  /* ERROR: next statement causes a server crash */
+  rc= mysql_stmt_execute(stmt);
+  check_execute(stmt, rc);
+
+  mysql_stmt_close(stmt);
+
+  rc= mysql_query(mysql, "drop table t1, t2");
+  myquery(rc);
+}
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */
@@ -14298,6 +14420,7 @@ static struct my_tests_st my_tests[]= {
   { "test_bug10760", test_bug10760 },
   { "test_bug12001", test_bug12001 },
   { "test_bug11909", test_bug11909 },
+  { "test_bug11901", test_bug11901 },
   { 0, 0 }
 };