Merge with 3.23:

Remove duplicate casedn_str() in mysql_change_db()
Fix for null handling in CASE

innobase/btr/btr0sea.c

@@ -453,8 +453,6 @@ btr_search_info_update_slow(
 	}
 
 	if (build_index) {
-		ut_a(block->n_fields + block->n_bytes > 0);	
-
 		btr_search_build_page_hash_index(block->frame,
 						block->n_fields,
 						block->n_bytes,
@@ -1028,7 +1026,10 @@ btr_search_build_page_hash_index(
 		return;
 	}
 
-	ut_a(n_fields + n_bytes > 0);
+	if (n_fields + n_bytes == 0) {
+
+	        return;
+	}
 
 	/* Calculate and cache fold values and corresponding records into
 	an array for fast insertion to the hash index */

mysql-test/r/case.result

@@ -63,3 +63,7 @@ nothing	2
 one	1
 two	1
 drop table t1;
+color
+orange
+yellow
+green

mysql-test/t/case.test

@@ -30,3 +30,8 @@ insert into t1 values(1),(2),(3),(4);
 select case a when 1 then 2 when 2 then 3 else 0 end as fcase, count(*) from t1 group by fcase;
 select case a when 1 then "one" when 2 then "two" else "nothing" end as fcase, count(*) from t1 group by fcase;
 drop table t1;
+drop table if exists t;
+create table t1 (row int not null, col int not null, val varchar(255) not null);
+insert into t1 values (1,1,'orange'),(1,2,'large'),(2,1,'yellow'),(2,2,'medium'),(3,1,'green'),(3,2,'small');
+select max(case col when 1 then val else null end) as color from t1 group by row;
+drop table if exists t;

sql/ha_innodb.cc

@@ -1238,7 +1238,14 @@ ha_innobase::open(
 	        if (primary_key != MAX_KEY) {
 	                fprintf(stderr,
 		    "InnoDB: Error: table %s has no primary key in InnoDB\n"
-		    "InnoDB: data dictionary, but has one in MySQL!\n", name);
+		    "InnoDB: data dictionary, but has one in MySQL!\n"
+		    "InnoDB: If you created the table with a MySQL\n"
+                    "InnoDB: version < 3.23.54 and did not define a primary\n"
+                    "InnoDB: key, but defined a unique key with all non-NULL\n"
+                    "InnoDB: columns, then MySQL internally treats that key\n"
+                    "InnoDB: as the primary key. You can fix this error by\n"
+		    "InnoDB: dump + DROP + CREATE + reimport of the table.\n",
+				name);
 		}
 
 		((row_prebuilt_t*)innobase_prebuilt)

sql/item_cmpfunc.cc

@@ -727,8 +727,9 @@ String *Item_func_case::val_str(String *str)
     null_value=1;
     return 0;
   }
+  null_value= 0;
   if (!(res=item->val_str(str)))
-    null_value=1;
+    null_value= 1;
   return res;
 }
 

sql/sql_db.cc

@@ -383,8 +383,6 @@ bool mysql_change_db(THD *thd,const char *name)
   }
   send_ok(&thd->net);
   x_free(thd->db);
-  if (lower_case_table_names)
-    casedn_str(dbname);
   thd->db=dbname;
   thd->db_length=db_length;
   thd->db_access=db_access;