vincenthe1

摘要： select * from world.country; select *from world.city; select *from world.countrylanguage; /*分组与排序*/select continent, count(*) as num_countryfrom world 阅读全文

摘要： select * from world.country; /*新建一列，upper将文本全部转为大写 lower全部转为小写*/select district, upper(district) as district_upcasefrom world.cityorder by district; / 阅读全文

摘要： /*用or 一样可以到达此效果，但用in操作符更好*/select governmentform, name, gnpfrom world.countrywhere Continent in ('aisa', 'europe'); /*通配符*//* %百分号表示任何字符出现任何次数，_下划线用途相 阅读全文

摘要： 2017-11-21 17:51:04 select * from world.city; select countrycode from world.city; /*distinct关键字作用于所有列，不仅仅跟着的后面那列*/select distinct countrycode from wor 阅读全文