Select region,name from world.country;

返回Region列和name列

Select * from world.country;

返回所有列

select distinct region from world.country;

返回不同的值

select region from world.country

limit 5 offset 10;

限制返回第10行起的後面5行資料

（第一個被檢索的是第0行）

select  region from world.country

order by region;

排序（升序）

select  region,name from world.country

order by region,name;

首先按region排序，在相同的region中再按name進行排序（升序）

select  region from world.country

order by region desc;

排序（降序）

select  region from world.country

where region="western europe";

過濾

select * from world.country

where indepyear between 1918 and 1962;

1918<=Indepyear<=1962

where indepyear is null

不包含值的

select * from world.country

where indepyear between 1918 and 1962 and population>14786000;

兩個過濾條件

select  region from world.country

where region="western europe" or region="south america";

滿足其中一個過濾條件

（and優先順序比or更高，組合使用需要加括號）

select  region from world.country

where region in("western europe","south america");

X = In(a,b,c,…)等價於X=a or X=b or X=c…

where region not in("western europe","south america");

相當於取反

where region like 'Ca%';

Like是萬用字元，%表示出現任意次數

找出所有由Ca開頭的region，不需要準確給出匹配的值

%Ca%匹配任意位置上包含Ca的值，不論前後出現了什麼字元

select  concat(region,' | ',name) from world.country

Concat(a,b,c,…)拼接a,b,c

select  concat(region,' | ',name) as new_column from world.country

拼接後按照new_column（別名）這一列來返回，任何客戶端都可以使用這一列

select  Avg(Population*IndepYear) as avg_column from world.country

求出Population*IndepYear的平均值，別名為avg_column

select  count(Population) as count_column from world.country

對有population值的行計數

select  max(Population) as max_column from world.country

返回population的最大值

select sum(Population>=0) as sum_column from world.country;

返回Population>=0的行數之和

select sum(Population) as sum_column from world.country;

返回所有的population之和

select sum(distinct Population) as sum_column from world.country;

返回所有不同的poulation的和（預設為all）

select region, count(*) as count_column from world.country

group by region;

按照region分組，然後計算每個組內包含的行數

select region,count(*) as count_column from world.country

group by region

having count_column>5;

Having類似於where，不同的是where過濾的物件是行，而having過濾的物件是分組，只顯示count_column大於5的分組

alter table world.country add sex int;

增加一列，列名為add，資料的型別為int

alter table world.country drop sex;

刪除sex這一列

alter table world.country modify population  int ;

更改population列的屬性

alter table world.country change column population abc int;

修改population列名為abc，int為屬性

update world.country set population=0 where code="aia";

更新where找出的行的population值為0