fix for Bug#46897 'Test "index_merge_innodb" fails (mostly)':

that was already analyzed by Oracle: EXPLAIN can return 3 or 4 in "rows"; using replace_column to work around this.

mysql-test/include/index_merge2.inc:
  replace "rows" column of some EXPLAINs by "#", if told so
mysql-test/r/index_merge_innodb.result:
  result update
mysql-test/t/index_merge_innodb.test:
  tell index_merge2.inc to accept random "rows" values in some EXPLAINs; we don't do this in index_merge_myisam.test
  which has no randomness here.

mysql-test/include/index_merge2.inc

@@ -122,12 +122,20 @@ insert into t1 (key1a, key1b, key2a, key2b, key3a, key3b)
 analyze table t1;
 select count(*) from t1;
 
+if ($index_merge_random_rows_in_EXPLAIN)
+{
+  --replace_column 9 #
+}
 explain select count(*) from t1 where
   key1a = 2 and key1b is null and  key2a = 2 and key2b is null;
 
 select count(*) from t1 where
   key1a = 2 and key1b is null and key2a = 2 and key2b is null;
 
+if ($index_merge_random_rows_in_EXPLAIN)
+{
+  --replace_column 9 #
+}
 explain select count(*) from t1 where
   key1a = 2 and key1b is null and key3a = 2 and key3b is null;
 

mysql-test/r/index_merge_innodb.result

@@ -111,7 +111,7 @@ count(*)
 explain select count(*) from t1 where
 key1a = 2 and key1b is null and  key2a = 2 and key2b is null;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index_merge	i1,i2	i1,i2	10,10	NULL	4	Using intersect(i1,i2); Using where; Using index
+1	SIMPLE	t1	index_merge	i1,i2	i1,i2	10,10	NULL	#	Using intersect(i1,i2); Using where; Using index
 select count(*) from t1 where
 key1a = 2 and key1b is null and key2a = 2 and key2b is null;
 count(*)
@@ -119,7 +119,7 @@ count(*)
 explain select count(*) from t1 where
 key1a = 2 and key1b is null and key3a = 2 and key3b is null;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index_merge	i1,i3	i1,i3	10,10	NULL	4	Using intersect(i1,i3); Using where; Using index
+1	SIMPLE	t1	index_merge	i1,i3	i1,i3	10,10	NULL	#	Using intersect(i1,i3); Using where; Using index
 select count(*) from t1 where
 key1a = 2 and key1b is null and key3a = 2 and key3b is null;
 count(*)

mysql-test/t/index_merge_innodb.test

@@ -12,6 +12,12 @@
 
 --source include/have_innodb.inc
 let $engine_type= InnoDB;
+# According to Oracle: "InnoDB's estimate for the index cardinality
+# depends on a pseudo random number generator (it picks up random
+# pages to sample). After an optimization that was made in r2625 two
+# EXPLAINs started returning a different number of rows (3 instead of
+# 4)", so:
+let $index_merge_random_rows_in_EXPLAIN = 1;
 # InnoDB does not support Merge tables (affects include/index_merge1.inc)
 let $merge_table_support= 0;