在我添加第二个左连接之前，下面的select工作得很好。现在显示表格的时间是18秒。
当我使用group\u concat和group by时，它可以很好地处理这两个连接。创建视图没有帮助。表1和表2之间是一对多的关系，因此我需要使用group\u concat在每一行中都有唯一的ticketno。
是否可以编写此查询以更快地执行它？谢谢。

SELECT table1.TICKETNO,
table2.STARTTIMESTAMP,
group_concat(table2.ACTION),
table1.COMPLETION,
table3.MEASURE
FROM table1
LEFT JOIN table2 ON (table1.TICKETNO=table2.TICKETNO)
LEFT JOIN table3 ON (table1.ERRORCODE=table3.ERRCODE)
GROUP BY table1.TICKETNO

索引：

+----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table          | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table1         |          0 | PRIMARY  |            1 | TICKETNO    | A         |       21894 |     NULL | NULL   |      | BTREE      |         |               |
+----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

+-------------------+------------+----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table             | Non_unique | Key_name | Seq_in_index | Column_name    | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------+------------+----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table2            |          0 | PRIMARY  |            1 | TICKETNO       | A         |       76110 |     NULL | NULL   |      | BTREE      |         |               |
| table2            |          0 | PRIMARY  |            2 | STARTTIMESTAMP | A         |       76110 |     NULL | NULL   |      | BTREE      |         |               |
+-------------------+------------+----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

+----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table          | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table3         |          0 | PRIMARY  |            1 | SPRAS       | A         |           6 |     NULL | NULL   |      | BTREE      |         |               |
| table3         |          0 | PRIMARY  |            2 | ERRCODE     | A         |        1138 |     NULL | NULL   |      | BTREE      |         |               |
+----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

以下是对我的问题的解释：

+------+-------------+-------------------+------+---------------+---------+---------+------------------------------------+-------+-------------------------------------------------+
| id   | select_type | table             | type | possible_keys | key     | key_len | ref                                | rows  | Extra                                           |
+------+-------------+-------------------+------+---------------+---------+---------+------------------------------------+-------+-------------------------------------------------+
|    1 | SIMPLE      | table1            | ALL  | NULL          | NULL    | NULL    | NULL                               | 21894 | Using temporary; Using filesort                 |
|    1 | SIMPLE      | table2            | ref  | PRIMARY       | PRIMARY | 8       | mydb.table1.TICKETNO               |     1 |                                                 |
|    1 | SIMPLE      | table3            | ALL  | NULL          | NULL    | NULL    | NULL                               |  1138 | Using where; Using join buffer (flat, BNL join) |
+------+-------------+-------------------+------+---------------+---------+---------+------------------------------------+-------+-------------------------------------------------+