MDEV-7836: ANALYZE FORMAT=JSON should provide info about GROUP/ORDER BY

Fix EXPLAIN FORMAT=JSON to produce output that's not worse than
the tabular form.

mysql-test/r/analyze_stmt_orderby.result

@@ -169,6 +169,7 @@ EXPLAIN
 {
   "query_block": {
     "select_id": 1,
+    "filesort": {
       "temporary_table": {
         "function": "buffer",
         "table": {
@@ -191,6 +192,7 @@ EXPLAIN
         }
       }
     }
+  }
 }
 analyze format=json
 select * from t0,t2 where t2.a=t0.a order by t2.b limit 4;
@@ -240,6 +242,36 @@ select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	10	Using where; Using filesort
 1	SIMPLE	t2	ref	a	a	5	test.t0.a	1	
+explain format=json
+select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "read_sorted_file": {
+      "filesort": {
+        "table": {
+          "table_name": "t0",
+          "access_type": "ALL",
+          "rows": 10,
+          "filtered": 100,
+          "attached_condition": "(t0.a is not null)"
+        }
+      }
+    },
+    "table": {
+      "table_name": "t2",
+      "access_type": "ref",
+      "possible_keys": ["a"],
+      "key": "a",
+      "key_length": "5",
+      "used_key_parts": ["a"],
+      "ref": ["test.t0.a"],
+      "rows": 1,
+      "filtered": 100
+    }
+  }
+}
 analyze format=json 
 select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;
 ANALYZE

mysql-test/r/explain_json.result

@@ -479,6 +479,7 @@ EXPLAIN
       "materialized": {
         "query_block": {
           "select_id": 2,
+          "filesort": {
             "temporary_table": {
               "function": "buffer",
               "table": {
@@ -492,6 +493,7 @@ EXPLAIN
         }
       }
     }
+  }
 }
 explain format=json
 select * from (select a, count(*) as cnt from t1 group by a) as tbl1, t1 as
@@ -521,6 +523,7 @@ EXPLAIN
       "materialized": {
         "query_block": {
           "select_id": 2,
+          "filesort": {
             "temporary_table": {
               "function": "buffer",
               "table": {
@@ -534,6 +537,7 @@ EXPLAIN
         }
       }
     }
+  }
 }
 #
 # Non-merged semi-join (aka JTBM)

mysql-test/r/explain_json_format_partitions.result

@@ -48,25 +48,28 @@ ANALYZE
 {
   "query_block": {
     "select_id": 1,
+    "r_total_time_ms": "REPLACED",
+    "buffer": {
       "table": {
         "update": 1,
         "table_name": "t1",
         "partitions": ["p0"],
         "access_type": "ALL",
         "rows": 10,
-      "r_rows": 3,
-      "r_filtered": 100,
-      "using_io_buffer": 1,
+        "r_rows": 10,
+        "r_filtered": 30,
         "r_total_time_ms": "REPLACED",
         "attached_condition": "(t1.a in (2,3,4))"
       }
     }
+  }
 }
 analyze format=json delete from t1 where a in (20,30,40);
 ANALYZE
 {
   "query_block": {
     "select_id": 1,
+    "r_total_time_ms": "REPLACED",
     "table": {
       "delete": 1,
       "table_name": "t1",

mysql-test/t/analyze_stmt_orderby.test

@@ -63,8 +63,8 @@ select * from t0,t2 where t2.a=t0.a order by t2.b limit 4;
 --echo #
 explain
 select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;
-## explain format=json
-## select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;
+explain format=json
+select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;
 --replace_regex /"r_total_time_ms": [0-9]*[.]?[0-9]*/"r_total_time_ms": "REPLACED"/
 analyze format=json 
 select * from t0,t2 where t2.a=t0.a order by t0.a limit 4;

sql/sql_explain.cc

@@ -818,9 +818,19 @@ void Explain_select::print_explain_json(Explain_query *query,
       if (using_temporary)
       {
         started_objects= 1;
+        if (using_filesort)
+        {
+          started_objects++;
+          writer->add_member("filesort").start_object();
+        }
         writer->add_member("temporary_table").start_object();
         writer->add_member("function").add_str("buffer");
       }
+      else
+      {
+        if (using_filesort)
+          first_table_sort= &ops_tracker.filesort_tracker[0];
+      }
     }
       
     Explain_basic_join::print_explain_json_interns(query, writer, is_analyze,
@@ -1293,7 +1303,12 @@ void add_json_keyset(Json_writer *writer, const char *elem_name,
 
 /*
   @param fs_tracker   Normally NULL. When not NULL, it means that the join tab
-                      used filesort.
+                      used filesort to pre-sort the data. Then, sorted data 
+                      was read and the rest of the join was executed.
+
+  @note
+  EXPLAIN command will check whether fs_tracker is present, but it can't use 
+  any value from fs_tracker (these are only valid for ANALYZE).
 */
 
 void Explain_table_access::print_explain_json(Explain_query *query,
@@ -1330,6 +1345,7 @@ void Explain_table_access::print_explain_json(Explain_query *query,
       }
     }
     writer->add_member("filesort").start_object();
+    if (is_analyze)
       fs_tracker->print_json(writer);
   }