BUG#20357 - Got error 124 from storage engine using MIN and MAX

            functions in queries

Using MAX()/MIN() on table with disabled indexes (by ALTER TABLE)
results in error 124 (wrong index) from storage engine.

The problem was that optimizer use disabled index to optimize
MAX()/MIN(). Normally it must skip disabled index and perform
table scan.

This patch skips disabled indexes for min/max optimization.

mysql-test/r/myisam.result

@@ -748,3 +748,16 @@ select count(id1) from t1 where id2 = 10;
 count(id1)
 5
 drop table t1;
+CREATE TABLE t1(a TINYINT, KEY(a)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES(1);
+SELECT MAX(a) FROM t1 IGNORE INDEX(a);
+MAX(a)
+1
+ALTER TABLE t1 DISABLE KEYS;
+SELECT MAX(a) FROM t1;
+MAX(a)
+1
+SELECT MAX(a) FROM t1 IGNORE INDEX(a);
+MAX(a)
+1
+DROP TABLE t1;

mysql-test/t/myisam.test

@@ -705,4 +705,16 @@ select count(*)   from t1 where id2 = 10;
 select count(id1) from t1 where id2 = 10;
 drop table t1;
 
+#
+# BUG##20357 - Got error 124 from storage engine using MIN and MAX functions
+#              in queries
+#
+CREATE TABLE t1(a TINYINT, KEY(a)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES(1);
+SELECT MAX(a) FROM t1 IGNORE INDEX(a);
+ALTER TABLE t1 DISABLE KEYS;
+SELECT MAX(a) FROM t1;
+SELECT MAX(a) FROM t1 IGNORE INDEX(a);
+DROP TABLE t1;
+
 # End of 4.1 tests

sql/opt_sum.cc

@@ -673,6 +673,12 @@ static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref,
   {
     KEY_PART_INFO *part,*part_end;
     key_part_map key_part_to_use= 0;
+    /*
+      Perform a check if index is not disabled by ALTER TABLE
+      or IGNORE INDEX.
+    */
+    if (!table->keys_in_use_for_query.is_set(idx))
+      continue;
     uint jdx= 0;
     *prefix_len= 0;
     for (part= keyinfo->key_part, part_end= part+keyinfo->key_parts ;