MDEV-27204: fixed Explain_basic_join::print_explain_json_interns "duplicates_removal" arraysbb-10.8-MDEV-27204

3 files changed, 101 insertions, 13 deletions

diff --git a/mysql-test/main/explain_json.result b/mysql-test/main/explain_json.result
index 35f2d11c8b6..a16c20c722e 100644
--- a/mysql-test/main/explain_json.result
+++ b/mysql-test/main/explain_json.result
@@ -842,20 +842,22 @@ EXPLAIN
         }
       },
       {
-        "duplicates_removal": {
-          "block-nl-join": {
-            "table": {
-              "table_name": "t1",
-              "access_type": "ALL",
-              "rows": 10,
-              "filtered": 100
-            },
-            "buffer_type": "flat",
-            "buffer_size": "206",
-            "join_type": "BNL",
-            "attached_condition": "t1.b = t2.b and t1.a = t2.a"
+        "duplicates_removal": [
+          {
+            "block-nl-join": {
+              "table": {
+                "table_name": "t1",
+                "access_type": "ALL",
+                "rows": 10,
+                "filtered": 100
+              },
+              "buffer_type": "flat",
+              "buffer_size": "206",
+              "join_type": "BNL",
+              "attached_condition": "t1.b = t2.b and t1.a = t2.a"
+            }
           }
-        }
+        ]
       }
     ]
   }
@@ -1941,3 +1943,77 @@ EXPLAIN
   }
 }
 drop table t1;
+#
+# MDEV-27204: [ERROR] Json_writer: a member name was expected, Assertion `got_name == named_item_expected()' failed
+#
+CREATE TABLE t (a INT);
+INSERT INTO t VALUES (1),(2);
+ANALYZE FORMAT=JSON SELECT * FROM t t1 WHERE t1.a IN (SELECT t2.a FROM t t2 WHERE t1.a IN (SELECT t3.a FROM t t3));
+ANALYZE
+{
+  "query_block": {
+    "select_id": 1,
+    "r_loops": 1,
+    "r_total_time_ms": 0.232912336,
+    "nested_loop": [
+      {
+        "table": {
+          "table_name": "t1",
+          "access_type": "ALL",
+          "r_loops": 1,
+          "rows": 2,
+          "r_rows": 2,
+          "r_table_time_ms": 0.006411025,
+          "r_other_time_ms": 0.008193918,
+          "filtered": 100,
+          "r_filtered": 100
+        }
+      },
+      {
+        "duplicates_removal": [
+          {
+            "block-nl-join": {
+              "table": {
+                "table_name": "t2",
+                "access_type": "ALL",
+                "r_loops": 1,
+                "rows": 2,
+                "r_rows": 2,
+                "r_table_time_ms": 0.002642007,
+                "r_other_time_ms": 0.008905227,
+                "filtered": 100,
+                "r_filtered": 100
+              },
+              "buffer_type": "flat",
+              "buffer_size": "152",
+              "join_type": "BNL",
+              "attached_condition": "t2.a = t1.a",
+              "r_filtered": 50
+            }
+          },
+          {
+            "block-nl-join": {
+              "table": {
+                "table_name": "t3",
+                "access_type": "ALL",
+                "r_loops": 1,
+                "rows": 2,
+                "r_rows": 2,
+                "r_table_time_ms": 0.001986124,
+                "r_other_time_ms": 0.027962783,
+                "filtered": 100,
+                "r_filtered": 100
+              },
+              "buffer_type": "incremental",
+              "buffer_size": "109",
+              "join_type": "BNL",
+              "attached_condition": "t3.a = t1.a",
+              "r_filtered": 50
+            }
+          }
+        ]
+      }
+    ]
+  }
+}
+DROP TABLE t;
diff --git a/mysql-test/main/explain_json.test b/mysql-test/main/explain_json.test
index cfbc0cfa10c..8c96fb07107 100644
--- a/mysql-test/main/explain_json.test
+++ b/mysql-test/main/explain_json.test
@@ -419,3 +419,11 @@ explain format=json select * from t1 order by a desc, b desc;
 explain format=json select * from t1 order by a desc, b ;
 drop table t1;
 
+--echo #
+--echo # MDEV-27204: [ERROR] Json_writer: a member name was expected, Assertion `got_name == named_item_expected()' failed
+--echo #
+
+CREATE TABLE t (a INT);
+INSERT INTO t VALUES (1),(2); 
+ANALYZE FORMAT=JSON SELECT * FROM t t1 WHERE t1.a IN (SELECT t2.a FROM t t2 WHERE t1.a IN (SELECT t3.a FROM t t3));
+DROP TABLE t;
diff --git a/sql/sql_explain.cc b/sql/sql_explain.cc
index 44654dc2e3d..4fd4e6d3b77 100644
--- a/sql/sql_explain.cc
+++ b/sql/sql_explain.cc
@@ -1100,12 +1100,16 @@ print_explain_json_interns(Explain_query *query,
       {
         writer->start_object();
         writer->add_member("duplicates_removal");
+        writer->start_array();
       }
 
       join_tabs[i]->print_explain_json(query, writer, is_analyze);
 
       if (join_tabs[i]->end_dups_weedout)
+      {
+        writer->end_array();
         writer->end_object();
+      }
     }
   } // "nested_loop"
   print_explain_json_for_children(query, writer, is_analyze);