MySQL部分从库上面因为大量的临时表tmp_table造成慢查询

背景描述

# Time: 2019-01-24T00:08:14.705724+08:00
# User@Host: **[**] @  [**]  Id: **
# Schema: sentrymeta  Last_errno: 0  Killed: 0
# Query_time: 0.315758  Lock_time: 0.001693  Rows_sent: 9664  Rows_examined: 36413  Rows_affected: 0
# Bytes_sent: 1616970  Tmp_tables: 1  Tmp_disk_tables: 1  Tmp_table_sizes: 16384
# QC_Hit: No  Full_scan: No  Full_join: No  Tmp_table: Yes  Tmp_table_on_disk: Yes
# Filesort: No  Filesort_on_disk: No  Merge_passes: 0
#   InnoDB_IO_r_ops: 0  InnoDB_IO_r_bytes: 0  InnoDB_IO_r_wait: 0.000000
#   InnoDB_rec_lock_wait: 0.000000  InnoDB_queue_wait: 0.000000
#   InnoDB_pages_distinct: 1085

             total       used       free     shared    buffers     cached
Mem:
-/+ buffers/cache:
Swap:                              

root@(none)04:33:02>select version();
+---------------+
| version()     |
+---------------+
| 5.7.19-17-log |
+---------------+
1 row in set (0.00 sec)

root@(none)04:33:07>show variables like '%table_size%';
+---------------------+-----------+
| Variable_name       | Value     |
+---------------------+-----------+
| max_heap_table_size | 134217728 |
| tmp_table_size      | 16777216  |
+---------------------+-----------+
2 rows in set (0.00 sec)

问题分析

Q1：为什么会产生临时表？

这个不多说，SQL写的惹不起，反正就是半个小时看不懂的那种，就是一眼就知道一定会产生临时表的