当面试官问你有关sql优化的问题时，直接拿笔写给他：
8-select 9-distinct<column_list>
1-from left_table
3-<join_type> join right_table
2-on <join_condition>
4-where <where_condition>
5-with <cube | rollup>
6-group by <column_list>
7-having <having_condition>
10-order by <column_list>
11-limit/rownum <number>
再补充 在关键字段加索引，避免全表扫描，防止判断条件时隐式转换；深入点数据库分区，表分区。。