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サブクエリ最適化の検証.txt
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サブクエリ最適化の検証.txt
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------------------------------------------------------------
■環境構築
- employeeデータベースをダウンロード
http://dev.mysql.com/doc/index-other.html
=> "Example Databases" -> "employee data (large dataset, includes data and test/verification suite)"
- employeeデータベースのセットアップ例
C:\Users\yyamasak> cd employees_db
C:\Users\yyamasak\employees_db> mysql -u root -p < employees.sql
Enter password: ****
- employeeデータベースのセットアップ手順書(マニュアル)
http://dev.mysql.com/doc/employee/en/employees-installation.html
------------------------------------------------------------
[実行するクエリー]
■サブクエリを使用
select emp_no,salary,from_date,to_date from salaries where emp_no in (select emp_no from employees where hire_date < '1985-12-31');
■サブクエリをJOINに書換え
select s.emp_no,s.salary,s.from_date,s.to_date from salaries s INNER JOIN employees e ON (s.emp_no=e.emp_no) where e.hire_date < '1985-12-31';
------------------------------------------------------------
[実行時間比較]
------------------------------------------------------------
[MySQL 5.5]
■サブクエリを使用
mysql> select emp_no,salary,from_date,to_date from salaries where emp_no in (select emp_no from employees where hire_date < '1985-
12-31');
+--------+--------+------------+------------+
| emp_no | salary | from_date | to_date |
+--------+--------+------------+------------+
| 10002 | 65828 | 1996-08-03 | 1997-08-03 |
| 10002 | 65909 | 1997-08-03 | 1998-08-03 |
| 10002 | 67534 | 1998-08-03 | 1999-08-03 |
<snip>
+--------+--------+------------+------------+
441975 rows in set (4.68 sec)
mysql>
mysql> explain select emp_no,salary,from_date,to_date from salaries where emp_no in (select emp_no from employees where hire_date
< '1985-12-31');
+----+--------------------+-----------+-----------------+---------------+---------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-----------+-----------------+---------------+---------+---------+------+---------+-------------+
| 1 | PRIMARY | salaries | ALL | NULL | NULL | NULL | NULL | 2844513 | Using where |
| 2 | DEPENDENT SUBQUERY | employees | unique_subquery | PRIMARY | PRIMARY | 4 | func | 1 | Using where |
+----+--------------------+-----------+-----------------+---------------+---------+---------+------+---------+-------------+
2 rows in set (0.00 sec)
mysql>
★★★★★★ EXPLAIN結果に"DEPENDENT SUBQUERY"が表示されている(※) ★★★★★★
※参考：なぜMySQLのサブクエリは遅いのか。
http://nippondanji.blogspot.jp/2009/03/mysql_25.html
■サブクエリをJOINに書換え
mysql> select s.emp_no,s.salary,s.from_date,s.to_date from salaries s INNER JOIN employees e ON (s.emp_no=e.emp_no) where e.hire_d
ate < '1985-12-31';
+--------+--------+------------+------------+
| emp_no | salary | from_date | to_date |
+--------+--------+------------+------------+
| 10002 | 65828 | 1996-08-03 | 1997-08-03 |
| 10002 | 65909 | 1997-08-03 | 1998-08-03 |
| 10002 | 67534 | 1998-08-03 | 1999-08-03 |
<snip>
+--------+--------+------------+------------+
441975 rows in set (0.71 sec)
★★★★★★ サブクエリをJOINに書替えることで高速化(MySQL 5.5までは、このようなチューニングが必要) ★★★★★★
mysql> explain select s.emp_no,s.salary,s.from_date,s.to_date from salaries s INNER JOIN employees e ON (s.emp_no=e.emp_no) where
e.hire_date < '1985-12-31';
+----+-------------+-------+------+----------------+---------+---------+--------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+----------------+---------+---------+--------------------+--------+-------------+
| 1 | SIMPLE | e | ALL | PRIMARY | NULL | NULL | NULL | 299920 | Using where |
| 1 | SIMPLE | s | ref | PRIMARY,emp_no | PRIMARY | 4 | employees.e.emp_no | 4 | |
+----+-------------+-------+------+----------------+---------+---------+--------------------+--------+-------------+
2 rows in set (0.00 sec)
[MySQL 5.6]
■サブクエリを使用
mysql> select emp_no,salary,from_date,to_date from salaries where emp_no in (select emp_no from employees where hire_date < '1985-
12-31');
+--------+--------+------------+------------+
| emp_no | salary | from_date | to_date |
+--------+--------+------------+------------+
| 10002 | 65828 | 1996-08-03 | 1997-08-03 |
| 10002 | 65909 | 1997-08-03 | 1998-08-03 |
| 10002 | 67534 | 1998-08-03 | 1999-08-03 |
<snip>
+--------+--------+------------+------------+
441975 rows in set (0.60 sec)
mysql>
★★★★★★ MySQL 5.6 の方が MySQL 5.5 よりも速い(0.60秒と4.68秒) ★★★★★★
mysql> explain select emp_no,salary,from_date,to_date from salaries where emp_no in (select emp_no from employees where hire_date
< '1985-12-31');
+----+-------------+-----------+------+----------------+---------+---------+----------------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+------+----------------+---------+---------+----------------------------+--------+-------------+
| 1 | SIMPLE | employees | ALL | PRIMARY | NULL | NULL | NULL | 299290 | Using where |
| 1 | SIMPLE | salaries | ref | PRIMARY,emp_no | PRIMARY | 4 | employees.employees.emp_no | 4 | NULL |
+----+-------------+-----------+------+----------------+---------+---------+----------------------------+--------+-------------+
2 rows in set (0.00 sec)
mysql>
★★★★★★ EXPLAIN結果に"DEPENDENT SUBQUERY"が無くなっている ★★★★★★
■サブクエリをJOINに書換え
mysql> select s.emp_no,s.salary,s.from_date,s.to_date from salaries s INNER JOIN employees e ON (s.emp_no=e.emp_no) where e.hire_d
ate < '1985-12-31';
+--------+--------+------------+------------+
| emp_no | salary | from_date | to_date |
+--------+--------+------------+------------+
| 10002 | 65828 | 1996-08-03 | 1997-08-03 |
| 10002 | 65909 | 1997-08-03 | 1998-08-03 |
| 10002 | 67534 | 1998-08-03 | 1999-08-03 |
<snip>
+--------+--------+------------+------------+
441975 rows in set (0.62 sec)
mysql>
mysql> explain select s.emp_no,s.salary,s.from_date,s.to_date from salaries s INNER JOIN employees e ON (s.emp_no=e.emp_no) where
e.hire_date < '1985-12-31';
+----+-------------+-------+------+----------------+---------+---------+--------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+----------------+---------+---------+--------------------+--------+-------------+
| 1 | SIMPLE | e | ALL | PRIMARY | NULL | NULL | NULL | 299290 | Using where |
| 1 | SIMPLE | s | ref | PRIMARY,emp_no | PRIMARY | 4 | employees.e.emp_no | 4 | NULL |
+----+-------------+-------+------+----------------+---------+---------+--------------------+--------+-------------+
2 rows in set (0.00 sec)
------------------------------------------------------------