SET optimizer_trace= 'enabled=on';

CREATE TABLE t1 (id INT PRIMARY KEY);

INSERT INTO t1 VALUES (1),(2);

CREATE TABLE t2 (a INT);

INSERT INTO t2 VALUES (3),(4);

SELECT * FROM t1 WHERE id < ( SELECT SUM(a) FROM t2 );

SELECT JSON_VALID(trace) FROM information_schema.optimizer_trace;

# Cleanup

DROP TABLE t1, t2;

SELECT * FROM t1 WHERE id < ( SELECT SUM(a) FROM t2 );

id

1

2

SELECT JSON_VALID(trace) FROM information_schema.optimizer_trace;

JSON_VALID(trace)

0

{

  "query_optimization": {

    "r_total_time_ms": 0.214919473

  },

  "query_block": {

    "select_id": 1,

    "r_loops": 1,

    "r_total_time_ms": 0.015704535,

    "nested_loop": [

      {

        "table": {

          "table_name": "t1",

          "access_type": "range",

          "possible_keys": ["PRIMARY"],

          "key": "PRIMARY",

          "key_length": "4",

          "used_key_parts": ["id"],

          "r_loops": 1,

          "rows": 2,

          "r_rows": 2,

          "r_table_time_ms": 0.004733423,

          "r_other_time_ms": 0.007802125,

          "filtered": 100,

          "r_filtered": 100,

          "attached_condition": "t1.`id` < (subquery#2)",

          "using_index": true

        }

      }

    ],

    "subqueries": [

      {

        "query_block": {

          "select_id": 2,

          "r_loops": 1,

          "r_total_time_ms": 0.019324802,

          "nested_loop": [

            {

              "table": {

                "table_name": "t2",

                "access_type": "ALL",

                "r_loops": 1,

                "rows": 2,

                "r_rows": 2,

                "r_table_time_ms": 0.00379075,

                "r_other_time_ms": 0.007952552,

                "filtered": 100,

                "r_filtered": 100

              }

            }

          ]

        }

      }

    ]

  }

{

  "substitute_best_equal": {

    "condition": "WHERE",

    "resulting_condition": "t1.`id` < (/* select#2 */ select #^B)"

  }

},

{

  "attaching_conditions_to_tables": {

    "attached_conditions_computation": [],

    "attached_conditions_summary": [

      {

        "table": "t1",

        "attached": "t1.`id` < (/* select#2 */ select #^B)"

      }

    ]

  }

}