MDEV-27699 ANALYZE FORMAT=JSON fields are incorrect for UNION ALL queries

UNION ALL queries are a subject of optimization introduced in MDEV-334
when creation of a temporary table is skipped.
While there is a check for this optimization in Explain_union::print_explain()
there was no such in Explain_union::print_explain_json(). This resulted in
printing irrelevant data like:
  "union_result": {
    "table_name": "<union2,3>",
    "access_type": "ALL",
    "r_loops": 0,
    "r_rows": null
in case when creation of the temporary table was actually optimized out.
This commits adds a check whether the temporary table was actually created
during the UNION ALL processing and eliminates printing of the irrelevant data.

mysql-test/main/cte_recursive.result

@@ -4050,10 +4050,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,4>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {

mysql-test/main/derived_cond_pushdown.result

@@ -10742,8 +10742,6 @@ EXPLAIN
       "materialized": {
         "query_block": {
           "union_result": {
-            "table_name": "<union2,3>",
-            "access_type": "ALL",
             "query_specifications": [
               {
                 "query_block": {
@@ -14718,8 +14716,6 @@ EXPLAIN
       "materialized": {
         "query_block": {
           "union_result": {
-            "table_name": "<union2,3>",
-            "access_type": "ALL",
             "query_specifications": [
               {
                 "query_block": {
@@ -14940,8 +14936,6 @@ EXPLAIN
       "materialized": {
         "query_block": {
           "union_result": {
-            "table_name": "<union2,3,4>",
-            "access_type": "ALL",
             "query_specifications": [
               {
                 "query_block": {

mysql-test/main/explain_json.result

@@ -247,8 +247,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {

mysql-test/main/table_value_constr.result

@@ -1304,8 +1304,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<unit1>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1525,8 +1523,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1589,8 +1585,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1633,8 +1627,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2,3>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1677,10 +1669,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<unit1>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {
@@ -1908,10 +1896,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {
@@ -1976,10 +1960,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {
@@ -2022,10 +2002,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2,3>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {

mysql-test/suite/compat/oracle/r/table_value_constr.result

@@ -1302,8 +1302,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<unit1>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1523,8 +1521,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1587,8 +1583,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1631,8 +1625,6 @@ EXPLAIN
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2,3>",
-      "access_type": "ALL",
       "query_specifications": [
         {
           "query_block": {
@@ -1675,10 +1667,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<unit1>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {
@@ -1906,10 +1894,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {
@@ -1974,10 +1958,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {
@@ -2020,10 +2000,6 @@ ANALYZE
 {
   "query_block": {
     "union_result": {
-      "table_name": "<union1,2,3>",
-      "access_type": "ALL",
-      "r_loops": 0,
-      "r_rows": null,
       "query_specifications": [
         {
           "query_block": {

sql/sql_explain.cc

@@ -581,27 +581,29 @@ void Explain_union::print_explain_json(Explain_query *query,
   else
     writer->add_member("union_result").start_object();
 
-  // using_temporary_table
-  make_union_table_name(table_name_buffer);
-  writer->add_member("table_name").add_str(table_name_buffer);
-  writer->add_member("access_type").add_str("ALL"); // not very useful
-
-  /* r_loops (not present in tabular output) */
-  if (is_analyze)
+  if (using_tmp)
   {
-    writer->add_member("r_loops").add_ll(fake_select_lex_tracker.get_loops());
-  }
+    make_union_table_name(table_name_buffer);
+    writer->add_member("table_name").add_str(table_name_buffer);
+    writer->add_member("access_type").add_str("ALL"); // not very useful
 
-  /* `r_rows` */
-  if (is_analyze)
-  {
-    writer->add_member("r_rows");
-    if (fake_select_lex_tracker.has_scans())
-      writer->add_double(fake_select_lex_tracker.get_avg_rows());
-    else
-      writer->add_null();
-  }
+    /* r_loops (not present in tabular output) */
+    if (is_analyze)
+    {
+      writer->add_member("r_loops").add_ll(
+          fake_select_lex_tracker.get_loops());
+    }
 
+    /* `r_rows` */
+    if (is_analyze)
+    {
+      writer->add_member("r_rows");
+      if (fake_select_lex_tracker.has_scans())
+        writer->add_double(fake_select_lex_tracker.get_avg_rows());
+      else
+        writer->add_null();
+    }
+  }
   writer->add_member("query_specifications").start_array();
 
   for (int i= 0; i < (int) union_members.elements(); i++)