如何优化这个简单的连接查询？需要很长时间

Question

我不确定如何开始优化我的平台运行的高延迟 SQL 查询。除了减少数据集之外，我还可以做哪些事情？

SELECT ctm.* 
FROM compound_transaction_map ctm 
JOIN bustransaction_map btm ON ctm.transId = btm.transId 
WHERE btm.docId = ?

docId 由我的 DBWConnector 插入到 Java 代码中

主要问题是表的大小，compound_transaction_map 是776,387 条目，bustransaction_map 是3,252,772。我正在努力减少表大小，但只是想知道这个查询是否也是一个问题。

只是想从比我更有经验的人那里获得一些见解。我感谢你的帮助。

编辑：有关于transId和bustransaction_map.docID的索引

mysql> show index from compound_transaction_map;
+--------------------------+------------+------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table                    | Non_unique | Key_name               | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------------------+------------+------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| compound_transaction_map |          0 | PRIMARY                |            1 | id          | A         |      765804 |     NULL | NULL   |      | BTREE      |         |               |
| compound_transaction_map |          0 | UNQ_compoundId_transId |            1 | transId     | A         |      772560 |     NULL | NULL   |      | BTREE      |         |               |
| compound_transaction_map |          0 | UNQ_compoundId_transId |            2 | compoundId  | A         |      772560 |     NULL | NULL   |      | BTREE      |         |               |
| compound_transaction_map |          1 | transId                |            1 | transId     | A         |      772560 |     NULL | NULL   |      | BTREE      |         |               |
| compound_transaction_map |          1 | compoundId             |            1 | compoundId  | A         |      645871 |     NULL | NULL   |      | BTREE      |         |               |
| compound_transaction_map |          1 | companyId              |            1 | companyId   | A         |         625 |     NULL | NULL   |      | BTREE      |         |               |
+--------------------------+------------+------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

mysql> show index from bustransaction_map;
+--------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table              | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| bustransaction_map |          0 | PRIMARY  |            1 | id          | A         |     2869993 |     NULL | NULL   |      | BTREE      |         |               |
| bustransaction_map |          0 | docId    |            1 | docId       | A         |     2883521 |     NULL | NULL   | YES  | BTREE      |         |               |
| bustransaction_map |          1 | transId  |            1 | transId     | A         |     1019639 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)

mysql> EXPLAIN
    -> SELECT ctm.*
IN bustransaction_ma    -> FROM compound_transaction_map ctm
    -> JOIN bustransaction_map btm ON ctm.transId = btm.transId
    -> WHERE btm.docId = '62EFCD90-BC62-9984-0B20-4465528D6359';
+----+-------------+-------+------------+-------+---------------+-------+---------+-------+--------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key   | key_len | ref   | rows   | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+-------+---------+-------+--------+----------+-------------+
|  1 | SIMPLE      | btm   | NULL       | const | docId,transId | docId | 153     | const |      1 |   100.00 | NULL        |
|  1 | SIMPLE      | ctm   | NULL       | ALL   | NULL          | NULL  | NULL    | NULL  | 772560 |   100.00 | Using where |
+----+-------------+-------+------------+-------+---------------+-------+---------+-------+--------+----------+-------------+
2 rows in set, 1 warning (0.01 sec)

mysql> SHOW CREATE TABLE compound_transaction_map;
+--------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table                    | Create Table

                                                            |
+--------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| compound_transaction_map | CREATE TABLE `compound_transaction_map` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `compoundId` varchar(100) NOT NULL,
  `transId` varchar(100) NOT NULL,
  `companyId` bigint(20) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`),
  UNIQUE KEY `UNQ_compoundId_transId` (`transId`,`compoundId`),
  KEY `transId` (`transId`),
  KEY `compoundId` (`compoundId`),
  KEY `companyId` (`companyId`)
) ENGINE=InnoDB AUTO_INCREMENT=865326 DEFAULT CHARSET=latin1 |
+--------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SHOW CREATE TABLE bustransaction_map;
+--------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table              | Create Table
                                                                                                                |
+--------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| bustransaction_map | CREATE TABLE `bustransaction_map` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `transId` varchar(50) DEFAULT NULL,
  `docId` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `docId` (`docId`),
  KEY `transId` (`transId`)
) ENGINE=InnoDB AUTO_INCREMENT=13033253 DEFAULT CHARSET=utf8 |
+--------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> EXPLAIN select ctm.* from bustransaction_map btm join compound_transaction_map ctm force index (transId) on ctm.transId = btm.transId where btm.docId = '62EFCD90-BC62-9984-0B20-4465528D6359';
+----+-------------+-------+------------+-------+---------------+-------+---------+-------+--------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key   | key_len | ref   | rows   | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+-------+---------+-------+--------+----------+-------------+
|  1 | SIMPLE      | btm   | NULL       | const | docId,transId | docId | 153     | const |      1 |   100.00 | NULL        |
|  1 | SIMPLE      | ctm   | NULL       | ALL   | NULL          | NULL  | NULL    | NULL  | 772560 |   100.00 | Using where |
+----+-------------+-------+------------+-------+---------------+-------+---------+-------+--------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

Answer 1

MySQL 每个表只能使用一个索引。

explain

表明它选择使用

bustransaction_map.docId

上的索引来帮助解决

where docId = ?

； Bustransaction_map 是较大的表，因此它希望减少其行数。它在

compound_transaction_map

上不使用索引。

要解决这个问题，请在

(docId, transId)

的bustransaction_map上创建一个复合索引（顺序很重要）。 MySQL 可以将此索引用于任何仅具有

bustransaction_map.docId

功能的查询以及像您一样使用

bustransaction_map.docId

和

bustransaction_map.transId

的查询。

然后您可以将索引放在

docId

上，这是多余的。您还可以删除

compound_transaction_map.transId

上的单列索引，它与

(transId, compoundId)

上的复合索引是多余的。

---

一般来说，如果有两列，则可以使用两个索引覆盖包含它们任意组合的所有查询...

• A
• （B，A）