Explain MariaDB

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "tst_batch",
      "access_type": "ALL",
      "rows": 32,
      "filtered": 100,
      "attached_condition": "tst_batch.end_date is null"
    },
    "table": {
      "table_name": "tst_batch_test_case_1",
      "access_type": "ref",
      "possible_keys": ["batch_id"],
      "key": "batch_id",
      "key_length": "4",
      "used_key_parts": ["batch_id"],
      "ref": ["portail2.tst_batch.id"],
      "rows": 10,
      "filtered": 100
    },
    "table": {
      "table_name": "tst_batch_step_1",
      "access_type": "ref",
      "possible_keys": ["batch_test_case_id"],
      "key": "batch_test_case_id",
      "key_length": "4",
      "used_key_parts": ["batch_test_case_id"],
      "ref": ["portail2.tst_batch_test_case_1.id"],
      "rows": 15,
      "filtered": 100,
      "attached_condition": "trigcond(trigcond(tst_batch_test_case_1.`id` is not null))"
    },
    "subqueries": [
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 8,
            "outer_ref_condition": "tst_batch_test_case_1.`id` is not null",
            "table": {
              "table_name": "tst_batch_step",
              "access_type": "ref",
              "possible_keys": ["batch_test_case_id"],
              "key": "batch_test_case_id",
              "key_length": "4",
              "used_key_parts": ["batch_test_case_id"],
              "ref": ["portail2.tst_batch_test_case_1.id"],
              "rows": 15,
              "filtered": 100,
              "using_index": true
            }
          }
        }
      },
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 6,
            "table": {
              "table_name": "tst_batch_test_case",
              "access_type": "ref",
              "possible_keys": ["batch_id"],
              "key": "batch_id",
              "key_length": "4",
              "used_key_parts": ["batch_id"],
              "ref": ["portail2.tst_batch.id"],
              "rows": 10,
              "filtered": 100,
              "attached_condition": "!<in_optimizer>(tst_batch_test_case.`id`,<exists>(subquery#7))",
              "using_index": true
            },
            "subqueries": [
              {
                "query_block": {
                  "select_id": 7,
                  "table": {
                    "table_name": "tst_batch_step",
                    "access_type": "ref",
                    "possible_keys": ["batch_test_case_id"],
                    "key": "batch_test_case_id",
                    "key_length": "4",
                    "used_key_parts": ["batch_test_case_id"],
                    "ref": ["portail2.tst_batch_test_case.id"],
                    "rows": 15,
                    "filtered": 100,
                    "index_condition": "<cache>(tst_batch_test_case.`id`) = tst_batch_step.batch_test_case_id",
                    "attached_condition": "tst_batch_step.s_status is null"
                  }
                }
              }
            ]
          }
        }
      },
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 5,
            "table": {
              "table_name": "tst_batch_test_case",
              "access_type": "ref",
              "possible_keys": ["PRIMARY", "batch_id"],
              "key": "batch_id",
              "key_length": "4",
              "used_key_parts": ["batch_id"],
              "ref": ["portail2.tst_batch.id"],
              "rows": 10,
              "filtered": 100,
              "using_index": true
            },
            "table": {
              "table_name": "tst_batch_step",
              "access_type": "ref",
              "possible_keys": ["batch_test_case_id"],
              "key": "batch_test_case_id",
              "key_length": "4",
              "used_key_parts": ["batch_test_case_id"],
              "ref": ["portail2.tst_batch_test_case.id"],
              "rows": 15,
              "filtered": 100,
              "using_index": true
            }
          }
        }
      },
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 4,
            "table": {
              "table_name": "tst_batch_test_case",
              "access_type": "ref",
              "possible_keys": ["batch_id"],
              "key": "batch_id",
              "key_length": "4",
              "used_key_parts": ["batch_id"],
              "ref": ["portail2.tst_batch.id"],
              "rows": 10,
              "filtered": 100,
              "using_index": true
            }
          }
        }
      },
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 3,
            "table": {
              "table_name": "tst_batch_test_case",
              "access_type": "ref",
              "possible_keys": ["PRIMARY", "batch_id"],
              "key": "batch_id",
              "key_length": "4",
              "used_key_parts": ["batch_id"],
              "ref": ["portail2.tst_batch.id"],
              "rows": 10,
              "filtered": 100,
              "using_index": true
            },
            "table": {
              "table_name": "tst_batch_step",
              "access_type": "ref",
              "possible_keys": ["batch_test_case_id"],
              "key": "batch_test_case_id",
              "key_length": "4",
              "used_key_parts": ["batch_test_case_id"],
              "ref": ["portail2.tst_batch_test_case.id"],
              "rows": 15,
              "filtered": 100,
              "attached_condition": "tst_batch_step.s_status = 'Not Valid'"
            }
          }
        }
      },
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 2,
            "table": {
              "table_name": "tst_batch_test_case",
              "access_type": "ref",
              "possible_keys": ["PRIMARY", "batch_id"],
              "key": "batch_id",
              "key_length": "4",
              "used_key_parts": ["batch_id"],
              "ref": ["portail2.tst_batch.id"],
              "rows": 10,
              "filtered": 100,
              "using_index": true
            },
            "table": {
              "table_name": "tst_batch_step",
              "access_type": "ref",
              "possible_keys": ["batch_test_case_id"],
              "key": "batch_test_case_id",
              "key_length": "4",
              "used_key_parts": ["batch_test_case_id"],
              "ref": ["portail2.tst_batch_test_case.id"],
              "rows": 15,
              "filtered": 100,
              "attached_condition": "tst_batch_step.s_status = 'KO'"
            }
          }
        }
      }
    ]
  }
}