MDEV-9504: ANALYZE TABLE shows wrong 'rows' value for ORDER BY query

- Legacy code would set JOIN_TAB::limit only for EXPLAIN queries (this variable is only used when producing EXPLAIN output) - ANALYZE/SHOW EXPLAIN need to produce EXPLAIN output for non-EXPLAIN queries, too, so we should always set JOIN_TAB::limit.

Author: spetrunia

mysql-test/r/analyze_stmt_orderby.result

@@ -583,4 +583,28 @@ ANALYZE
  }
 }
 drop table t2;
-drop table t0,t1;
+drop table t1;
+#
+# MDEV-9504: ANALYZE TABLE shows wrong 'rows' value for ORDER BY query
+#
+create table t1 (
+a int, 
+filler1 char(128),
+filler2 char(128),
+key(a)
+);
+insert into t1 
+select A.a+10*B.a+100*C.a, repeat('abc-',32), repeat('abc-',32)
+from t0 A, t0 B, t0 C;
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Table is already up to date
+explain select a from t1 order by a limit 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	NULL	a	5	NULL	10	Using index
+# 'rows' in ANALYZE output must match 'rows' in EXPLAIN:
+analyze select a from t1 order by a limit 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
+1	SIMPLE	t1	index	NULL	a	5	NULL	10	10.00	100.00	100.00	Using index
+drop table t1;
+drop table t0;

mysql-test/t/analyze_stmt_orderby.test

@@ -174,4 +174,27 @@ select col1 f1, col2 f2, col1 f3 from t2 group by f1;
 drop table t2;
 
 
-drop table t0,t1;
+drop table t1;
+
+--echo #
+--echo # MDEV-9504: ANALYZE TABLE shows wrong 'rows' value for ORDER BY query
+--echo #
+create table t1 (
+ a int, 
+ filler1 char(128),
+ filler2 char(128),
+ key(a)
+);
+
+insert into t1 
+select A.a+10*B.a+100*C.a, repeat('abc-',32), repeat('abc-',32)
+from t0 A, t0 B, t0 C;
+analyze table t1;
+
+explain select a from t1 order by a limit 10;
+--echo # 'rows' in ANALYZE output must match 'rows' in EXPLAIN:
+analyze select a from t1 order by a limit 10;
+
+drop table t1;
+drop table t0;
+

sql/sql_select.cc

@@ -21031,12 +21031,14 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
  }
 
  table->file->ha_index_or_rnd_end();
+
+ if (select_limit < table->stat_records())
+ tab->limit= select_limit;
+
  if (tab->join->select_options & SELECT_DESCRIBE)
  {
  tab->ref.key= -1;
  tab->ref.key_parts= 0;
- if (select_limit < table->stat_records())
- tab->limit= select_limit;
  table->disable_keyread();
  }
  }