使用INNER JOIN时,MySQL不会对简单的查询做出响应.特别是“发送

发布时间：2020-12-12 16:28:25 所属栏目：MsSql教程来源：网络整理

导读：我有两张桌子具有48 959 281行的歌曲,以及5 721 117行的popular_songs. 这是两个表的结构： CREATE TABLE songs ( songId BIGINT(20) NOT NULL,songName VARCHAR(1000) NOT NULL,songDuration BIGINT(20) NOT NULL,songPreview VARCHAR(1000) NOT NULL,PRIMAR

我有两张桌子具有48 959 281行的歌曲,以及5 721 117行的popular_songs.

这是两个表的结构：

CREATE TABLE songs (
  songId       BIGINT(20)    NOT NULL,songName     VARCHAR(1000) NOT NULL,songDuration BIGINT(20)    NOT NULL,songPreview  VARCHAR(1000) NOT NULL,PRIMARY KEY (songId),INDEX (songDuration)
)
  ENGINE = InnoDB
  DEFAULT CHARSET = utf8
  DEFAULT COLLATE utf8_general_ci;

CREATE TABLE popular_songs (
  storeFrontId BIGINT(20) NOT NULL,genreId      BIGINT(20) NOT NULL,songId       BIGINT(20) NOT NULL,songRank     INT(11)    NOT NULL,INDEX (storeFrontId),INDEX (genreId),INDEX (songId),INDEX (songRank),CONSTRAINT popular_song UNIQUE (storeFrontId,genreId,songId),FOREIGN KEY (storeFrontId) REFERENCES storefront (storeFrontId),FOREIGN KEY (genreId) REFERENCES genre (genreId),FOREIGN KEY (songId) REFERENCES songs (songId)
)
  ENGINE = InnoDB
  DEFAULT CHARSET = utf8
  DEFAULT COLLATE utf8_general_ci;

当我在两个以下的运行时,一切都正常.

mysql> SELECT count(*) FROM songs;
+----------+
| count(*) |
+----------+
| 48959281 |
+----------+
1 row in set (9.10 sec)

mysql> SHOW PROFILE;
+--------------------------------+----------+
| Status                         | Duration |
+--------------------------------+----------+
| starting                       | 0.000008 |
| Waiting for query cache lock   | 0.000002 |
| checking query cache for query | 0.000019 |
| checking permissions           | 0.000003 |
| Opening tables                 | 0.000011 |
| System lock                    | 0.000004 |
| Waiting for query cache lock   | 0.000017 |
| init                           | 0.000006 |
| optimizing                     | 0.000003 |
| statistics                     | 0.000004 |
| preparing                      | 0.000004 |
| executing                      | 0.000003 |
| Sending data                   | 9.100444 |
| end                            | 0.000012 |
| query end                      | 0.000005 |
| closing tables                 | 0.000008 |
| freeing items                  | 0.000007 |
| Waiting for query cache lock   | 0.000002 |
| freeing items                  | 0.000012 |
| Waiting for query cache lock   | 0.000002 |
| freeing items                  | 0.000001 |
| storing result in query cache  | 0.000002 |
| logging slow query             | 0.000001 |
| cleaning up                    | 0.000003 |
+--------------------------------+----------+
24 rows in set (0.00 sec)

mysql> SELECT count(*) FROM popular_songs;
+----------+
| count(*) |
+----------+
|  5721117 |
+----------+
1 row in set (1.34 sec)

mysql> SHOW PROFILE;
+--------------------------------+----------+
| Status                         | Duration |
+--------------------------------+----------+
| starting                       | 0.000012 |
| Waiting for query cache lock   | 0.000004 |
| checking query cache for query | 0.000037 |
| checking permissions           | 0.000006 |
| Opening tables                 | 0.000017 |
| System lock                    | 0.000007 |
| Waiting for query cache lock   | 0.000031 |
| init                           | 0.000010 |
| optimizing                     | 0.000017 |
| statistics                     | 0.000004 |
| preparing                      | 0.000004 |
| executing                      | 0.000003 |
| Sending data                   | 1.343991 |
| end                            | 0.000010 |
| query end                      | 0.000005 |
| closing tables                 | 0.000007 |
| freeing items                  | 0.000007 |
| Waiting for query cache lock   | 0.000002 |
| freeing items                  | 0.000011 |
| Waiting for query cache lock   | 0.000001 |
| freeing items                  | 0.000001 |
| storing result in query cache  | 0.000002 |
| logging slow query             | 0.000001 |
| cleaning up                    | 0.000003 |
+--------------------------------+----------+
24 rows in set (0.00 sec)

当我运行这些以下查询时,MySQL没有响应.我不明白是什么原因.

SELECT COUNT(*)
FROM songs
INNER JOIN popular_songs ON popular_songs.songId = songs.songId

SELECT COUNT(*)
FROM songs
INNER JOIN popular_songs ON popular_songs.songId = songs.songId
WHERE songs.songDuration > 0

更新：

MySQL响应上面两个查询.但发送数据需要250-300秒.如何优化这个.

EXPLAIN EXTENDED报告：

mysql> EXPLAIN EXTENDED
    -> SELECT COUNT(*)
    -> FROM songs
    -> INNER JOIN popular_songs ON popular_songs.songId = songs.songId;
+----+-------------+---------------+--------+---------------+----------+---------+-----------------------------+---------+----------+-------------+
| id | select_type | table         | type   | possible_keys | key      | key_len | ref                         | rows    | filtered | Extra       |
+----+-------------+---------------+--------+---------------+----------+---------+-----------------------------+---------+----------+-------------+
|  1 | SIMPLE      | popular_songs | index  | songId        | songRank | 4       | NULL                        | 6449163 |   100.00 | Using index |
|  1 | SIMPLE      | songs         | eq_ref | PRIMARY       | PRIMARY  | 8       | itunes.popular_songs.songId |       1 |   100.00 | Using index |
+----+-------------+---------------+--------+---------------+----------+---------+-----------------------------+---------+----------+-------------+
2 rows in set,1 warning (0.01 sec)

mysql> EXPLAIN EXTENDED
    -> SELECT COUNT(*)
    -> FROM songs
    -> INNER JOIN popular_songs ON popular_songs.songId = songs.songId
    -> WHERE songs.songDuration > 0;
+----+-------------+---------------+--------+----------------------+----------+---------+-----------------------------+---------+----------+-------------+
| id | select_type | table         | type   | possible_keys        | key      | key_len | ref                         | rows    | filtered | Extra       |
+----+-------------+---------------+--------+----------------------+----------+---------+-----------------------------+---------+----------+-------------+
|  1 | SIMPLE      | popular_songs | index  | songId               | songRank | 4       | NULL                        | 6449163 |   100.00 | Using index |
|  1 | SIMPLE      | songs         | eq_ref | PRIMARY,songDuration | PRIMARY  | 8       | itunes.popular_songs.songId |       1 |   100.00 | Using where |
+----+-------------+---------------+--------+----------------------+----------+---------+-----------------------------+---------+----------+-------------+
2 rows in set,1 warning (0.00 sec)

当使用INDEX songId加入两个表时：

mysql> SELECT COUNT(*) FROM songs INNER JOIN popular_songs USE INDEX FOR JOIN (songId) ON popular_songs.songId = songs.songId;
+----------+
| COUNT(*) |
+----------+
|  5721117 |
+----------+
1 row in set (25.35 sec)

mysql> SHOW PROFILE;
+--------------------------------+-----------+
| Status                         | Duration  |
+--------------------------------+-----------+
| starting                       |  0.000011 |
| Waiting for query cache lock   |  0.000004 |
| checking query cache for query |  0.000045 |
| checking permissions           |  0.000004 |
| checking permissions           |  0.000004 |
| Opening tables                 |  0.000023 |
| System lock                    |  0.000007 |
| Waiting for query cache lock   |  0.000030 |
| init                           |  0.000021 |
| optimizing                     |  0.000011 |
| statistics                     |  0.000020 |
| preparing                      |  0.000012 |
| executing                      |  0.000005 |
| Sending data                   | 25.350160 |
| end                            |  0.000019 |
| query end                      |  0.000005 |
| closing tables                 |  0.000024 |
| freeing items                  |  0.000022 |
| Waiting for query cache lock   |  0.000002 |
| freeing items                  |  0.000016 |
| Waiting for query cache lock   |  0.000001 |
| freeing items                  |  0.000001 |
| storing result in query cache  |  0.000002 |
| logging slow query             |  0.000001 |
| logging slow query             |  0.000005 |
| cleaning up                    |  0.000003 |
+--------------------------------+-----------+
26 rows in set (0.00 sec)

这很漂亮但是,发送数据仍然需要25秒.

说明扩展以上查询：

mysql> EXPLAIN EXTENDED SELECT COUNT(*) FROM songs INNER JOIN popular_songs USE INDEX FOR JOIN (songId) ON popular_songs.songId = songs.songId;
+----+-------------+---------------+--------+---------------+---------+---------+-----------------------------+---------+----------+-------------+
| id | select_type | table         | type   | possible_keys | key     | key_len | ref                         | rows    | filtered | Extra       |
+----+-------------+---------------+--------+---------------+---------+---------+-----------------------------+---------+----------+-------------+
|  1 | SIMPLE      | popular_songs | index  | songId        | songId  | 8       | NULL                        | 2684407 |   100.00 | Using index |
|  1 | SIMPLE      | songs         | eq_ref | PRIMARY       | PRIMARY | 8       | itunes.popular_songs.songId |       1 |   100.00 | Using index |
+----+-------------+---------------+--------+---------------+---------+---------+-----------------------------+---------+----------+-------------+
2 rows in set,1 warning (0.00 sec)

解决方法

我猜测,songDuration的索引会让优化器混淆.你可以尝试这样查询：

SELECT COUNT(*)
FROM songs s
WHERE EXISTS (SELECT 1
              FROM popular_songs ps
              WHERE ps.songId = s.songId
             ) AND
      s.songDuration > 0;

songDuration的索引将更好地包括songId：歌曲(songDuration,songId).

（编辑：李大同）

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