BUG#32047 - 'Spurious' errors while opening MERGE tables

Accessing well defined MERGE table may return an error
stating that the merge table is incorrectly defined. This
happens if MERGE child tables were accessed before and we
failed to open another incorrectly defined MERGE table in
this connection.

myrg_open() internally used my_errno as a variable for determining
failure, and thus could be tricked into a wrong decision by other
uses of my_errno.

With this fix we use function local boolean flag instead of my_errno
to determine failure.

myisammrg/myrg_open.c

@@ -40,6 +40,7 @@ MYRG_INFO *myrg_open(const char *name, int mode, int handle_locking)
   IO_CACHE file;
   MI_INFO *isam=0;
   uint found_merge_insert_method= 0;
+  my_bool bad_children= FALSE;
   DBUG_ENTER("myrg_open");
 
   LINT_INIT(key_parts);
@@ -89,13 +90,13 @@ MYRG_INFO *myrg_open(const char *name, int mode, int handle_locking)
       fn_format(buff, buff, "", "", 0);
     if (!(isam=mi_open(buff,mode,(handle_locking?HA_OPEN_WAIT_IF_LOCKED:0))))
     {
-      my_errno= HA_ERR_WRONG_MRG_TABLE_DEF;
       if (handle_locking & HA_OPEN_FOR_REPAIR)
       {
         myrg_print_wrong_table(buff);
+        bad_children= TRUE;
         continue;
       }
-      goto err;
+      goto bad_children;
     }
     if (!m_info)                                /* First file */
     {
@@ -122,13 +123,13 @@ MYRG_INFO *myrg_open(const char *name, int mode, int handle_locking)
     files++;
     if (m_info->reclength != isam->s->base.reclength)
     {
-      my_errno=HA_ERR_WRONG_MRG_TABLE_DEF;
       if (handle_locking & HA_OPEN_FOR_REPAIR)
       {
         myrg_print_wrong_table(buff);
+        bad_children= TRUE;
         continue;
       }
-      goto err;
+      goto bad_children;
     }
     m_info->options|= isam->s->options;
     m_info->records+= isam->state->records;
@@ -141,8 +142,8 @@ MYRG_INFO *myrg_open(const char *name, int mode, int handle_locking)
                                      m_info->tables);
   }
 
-  if (my_errno == HA_ERR_WRONG_MRG_TABLE_DEF)
-    goto err;
+  if (bad_children)
+    goto bad_children;
   if (!m_info && !(m_info= (MYRG_INFO*) my_malloc(sizeof(MYRG_INFO),
                                                   MYF(MY_WME | MY_ZEROFILL))))
     goto err;
@@ -170,12 +171,14 @@ MYRG_INFO *myrg_open(const char *name, int mode, int handle_locking)
   pthread_mutex_unlock(&THR_LOCK_open);
   DBUG_RETURN(m_info);
 
+bad_children:
+  my_errno= HA_ERR_WRONG_MRG_TABLE_DEF;
 err:
   save_errno=my_errno;
   switch (errpos) {
   case 3:
     while (files)
-      mi_close(m_info->open_tables[--files].table);
+      (void) mi_close(m_info->open_tables[--files].table);
     my_free((char*) m_info,MYF(0));
     /* Fall through */
   case 2:

mysql-test/r/merge.result

@@ -940,4 +940,15 @@ m1	CREATE TABLE `m1` (
   `a` int(11) default NULL
 ) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, m1;
+CREATE TABLE t1(a INT);
+CREATE TABLE t2(a VARCHAR(10));
+CREATE TABLE m1(a INT) ENGINE=MERGE UNION=(t1, t2);
+CREATE TABLE m2(a INT) ENGINE=MERGE UNION=(t1);
+SELECT * FROM t1;
+a
+SELECT * FROM m1;
+ERROR HY000: Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist
+SELECT * FROM m2;
+a
+DROP TABLE t1, t2, m1, m2;
 End of 5.0 tests

mysql-test/t/merge.test

@@ -556,4 +556,17 @@ ALTER TABLE m1 UNION=();
 SHOW CREATE TABLE m1;
 DROP TABLE t1, m1;
 
+#
+# BUG#32047 - 'Spurious' errors while opening MERGE tables
+#
+CREATE TABLE t1(a INT);
+CREATE TABLE t2(a VARCHAR(10));
+CREATE TABLE m1(a INT) ENGINE=MERGE UNION=(t1, t2);
+CREATE TABLE m2(a INT) ENGINE=MERGE UNION=(t1);
+SELECT * FROM t1;
+--error ER_WRONG_MRG_TABLE
+SELECT * FROM m1;
+SELECT * FROM m2;
+DROP TABLE t1, t2, m1, m2;
+
 --echo End of 5.0 tests