show variables like ‘max_%‘;
| max_heap_table_size | 16777216 |
| max_tmp_tables | 32 |
show variables like ‘tmp_%‘;
| tmp_table_size | 1048576000 |
set global max_heap_table_size=1048576000
set global tmp_table_size=1048576000
原文：http://www.cnblogs.com/ahuo/p/5977698.html