MDEV-406: ANALYZE $stmt

- Testcase for ANALYZE UNION
- Provide r_rows for union result.

mysql-test/t/analyze_stmt.test

@@ -28,4 +28,11 @@ analyze update t1 set b=100+b where a in (6,7,8);
 select * from t1;
 drop table t1;
 
+--echo # Check that UNION works
+create table t1(a int, b int);
+insert into t1 select a,a from t0;
+analyze (select * from t1 A where a<5) union (select * from t1 B where a in (5,6));
+analyze (select * from t1 A where a<5) union (select * from t1 B where a in (1,2));
+drop table t1;
+
 drop table t0;

sql/sql_explain.cc

@@ -291,7 +291,11 @@ int Explain_union::print_explain(Explain_query *query,
   
   /* `r_rows` */
   if (is_analyze)
-    item_list.push_back(item_null);
+  {
+    ha_rows avg_rows= fake_select_lex_tracker.get_avg_rows();
+    item_list.push_back(new Item_int((longlong) (ulonglong) avg_rows,
+                                      MY_INT64_NUM_DECIMAL_DIGITS));
+  }
 
   /* `filtered` */
   if (explain_flags & DESCRIBE_EXTENDED || is_analyze)
@@ -542,7 +546,7 @@ int Explain_table_access::print_explain(select_result_sink *output, uint8 explai
   /* `r_rows` */
   if (is_analyze)
   {
-    ha_rows avg_rows= tracker.r_scans ? round((double) tracker.r_rows / tracker.r_scans): 0;
+    ha_rows avg_rows= tracker.get_avg_rows();
     item_list.push_back(new Item_int((longlong) (ulonglong) avg_rows,
                                       MY_INT64_NUM_DECIMAL_DIGITS));
   }

sql/sql_explain.h

@@ -27,6 +27,11 @@ class Table_access_tracker
   ha_rows r_rows; /* How many rows we've got after that */
   ha_rows r_rows_after_table_cond; /* Rows after applying the table condition */
   ha_rows r_rows_after_where; /* Rows after applying attached part of WHERE */
+
+  ha_rows get_avg_rows()
+  {
+    return r_scans ? round((double) r_rows / r_scans): 0;
+  }
 };