DEPENDENT SUBQUERY” 和 “SUBQUERY”

http://blog.163.com/li_hx/blog/static/183991413201642410122327/

mysql> CREATE TABLE t1 (a INT, b INT);
Query OK,  rows affected (0.22 sec)

mysql> CREATE TABLE t2 (c INT, d INT);
Query OK,  rows affected (0.21 sec)

mysql> CREATE TABLE t3 (e INT);
Query OK,  rows affected (0.22 sec)

mysql> INSERT INTO t1 VALUES (,), (,);
Query OK,  rows affected (0.19 sec)
Records:   Duplicates:   Warnings: 

mysql> INSERT INTO t2 VALUES (,), (,);
Query OK,  rows affected (0.17 sec)
Records:   Duplicates:   Warnings: 

mysql> INSERT INTO t3 VALUES (), ();
Query OK,  rows affected (0.18 sec)
Records:   Duplicates:   Warnings: 

mysql> select * from t1;
+------+------+
| a    | b    |
+------+------+
|     |    |
|     |    |
+------+------+
 rows in set (0.00 sec)

mysql> select * from t2;
+------+------+
| c    | d    |
+------+------+
|     |    |
|     |    |
+------+------+
 rows in set (0.00 sec)

mysql> select * from t3;
+------+
| e    |
+------+
|    |
|    |
+------+
 rows in set (0.00 sec)

mysql> EXPLAIN SELECT * FROM t1 WHERE t1.a IN (SELECT c FROM t2 WHERE (SELECT e FROM t3 as t31) < SOME (SELECT e FROM t3 as t32 WHERE t1.b));
+----+--------------------+-------+------+---------------+------+---------+------+------+--------------------------------------------------------------------+
| id | select_type        | table | type | possible_keys | key  | key_len | ref  | rows | Extra                                                              |
+----+--------------------+-------+------+---------------+------+---------+------+------+--------------------------------------------------------------------+
|   | PRIMARY            | t1    | ALL  | NULL          | NULL | NULL    | NULL |     | Using where                                                        |
|   | PRIMARY            | t2    | ALL  | NULL          | NULL | NULL    | NULL |     | Using where; FirstMatch(t1); Using join buffer (Block Nested Loop) |
|   | DEPENDENT SUBQUERY | t32   | ALL  | NULL          | NULL | NULL    | NULL |     | Using where                                                        |
|   | SUBQUERY           | t31   | ALL  | NULL          | NULL | NULL    | NULL |     | NULL                                                               |
+----+--------------------+-------+------+---------------+------+---------+------+------+--------------------------------------------------------------------+
 rows in set (0.00 sec)

mysql> EXPLAIN format=json SELECT * FROM t1 WHERE t1.a IN (SELECT c FROM t2 WHERE (SELECT e FROM t3 as t31) < SOME (SELECT e FROM t3 as t32 WHERE t1.b))\G
*************************** . row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": ,
    "nested_loop": [
      {
        "table": {
          "table_name": "t1",
          "access_type": "ALL",
          "rows": ,
          "filtered": ,
          "attached_condition": "<nop>(<in_optimizer>((/* select#3 */ select `test`.`t31`.`e` from `test`.`t3` `t31`),<exists>(/* select#4 */ select 1 from `test`.`t3` `t32` where (`test`.`t1`.`b` and <if>(outer_field_is_not_null, ((<cache>((/* select#3 */ select `test`.`t31`.`e` from `test`.`t3` `t31`)) < `test`.`t32`.`e`) or isnull(`test`.`t32`.`e`)), true)) having <if>(outer_field_is_not_null, <is_not_null_test>(`test`.`t32`.`e`), true))))",
          "attached_subqueries": [
            {
              "dependent": true,
              "cacheable": false,
              "query_block": {
                "select_id": ,
                "table": {
                  "table_name": "t32",
                  "access_type": "ALL",
                  "rows": ,
                  "filtered": ,
                  "attached_condition": "(`test`.`t1`.`b` and <if>(outer_field_is_not_null, ((<cache>((/* select#3 */ select `test`.`t31`.`e` from `test`.`t3` `t31`)) < `test`.`t32`.`e`) or isnull(`test`.`t32`.`e`)), true))"
                }
              }
            },
            {
              "dependent": false,
              "cacheable": true,
              "query_block": {
                "select_id": ,
                "table": {
                  "table_name": "t31",
                  "access_type": "ALL",
                  "rows": ,
                  "filtered":
                }
              }
            }
          ]
        }
      },
      {
        "table": {
          "table_name": "t2",
          "access_type": "ALL",
          "rows": ,
          "filtered": ,
          "first_match": "t1",
          "using_join_buffer": "Block Nested Loop",
          "attached_condition": "(`test`.`t2`.`c` = `test`.`t1`.`a`)"
        }
      }
    ]
  }
}
 row in set,  warnings (0.00 sec)

mysql> SHOW WARNINGS\G
*************************** . row ***************************
  Level: Note
   Code:
Message: Field or reference 'test.t1.b' of SELECT # was resolved in SELECT #
*************************** . row ***************************
  Level: Note
   Code:
Message: /* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` semi join (`test`.`t2`) where ((`test`.`t2`.`c` = `test`.`t1`.`a`) and <nop>(<in_optimizer>((/* select#3 */ select `test`.`t31`.`e` from `test`.`t3` `t31`),<exists>(/* select#4 */ select  from `test`.`t3` `t32` where (`test`.`t1`.`b` and <if>(outer_field_is_not_null, ((<cache>((/* select#3 */ select `test`.`t31`.`e` from `test`.`t3` `t31`)) < `test`.`t32`.`e`) or isnull(`test`.`t32`.`e`)), true)) having <if>(outer_field_is_not_null, <is_not_null_test>(`test`.`t32`.`e`), true)))))
 rows in set (0.00 sec)