全文搜索最慢
EXPLAIN select * from `city`;
范围搜索
EXPLAIN select * from `city` where ID>5 and ID<20; 
主键查询
EXPLAIN select * from `city`where ID=5; 
索引查询
EXPLAIN select * from `city`where CountryCode='NLD';
普通查询
EXPLAIN select * from `city` where Name='Haag';