获取指定线程正在执行SQL的执行计划信息，可以使用下面语句；
当某个线程执行SQL消耗了很长的时间，可以使用这个语句找到正在执行大SQL的执行计划，在性能诊断上很有用。
mysql> show processlist;
+----+------+-----------+------+---------+------+--------------+----------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+--------------+----------------------------------------------+
| 17 | root | localhost | NULL | Query | 0 | starting | show processlist |
| 18 | neo | localhost | fire | Query | 257 | Sending data | select count(*) from t1 join t2 on t1.a=t2.a |
+----+------+-----------+------+---------+------+--------------+----------------------------------------------+
2 rows in set (0.00 sec)
mysql>
EXPLAIN FOR CONNECTION 18;
+----+-------------+-------+------------+-------+---------------+----------+---------+-----------+--------+----------+--------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+----------+---------+-----------+--------+----------+--------------------------+
| 1 | SIMPLE | t1 | NULL | index | idx_t1_a | idx_t1_a | 5 | NULL | 392945 | 100.00 | Using where; Using index |
| 1 | SIMPLE | t2 | NULL | ref | idx_t2_a | idx_t2_a | 5 | fire.t1.a | 1 | 100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+----------+---------+-----------+--------+----------+--------------------------+
2 rows in set (0.00 sec)
