SQL 新人入門 （從基礎框架走起）SQL語句最基礎框架

select 欄位 from 表名

以下語句皆在該基礎上加內容，假設表名為table

①如果想搜尋表內所有內容

select * from table

②搜尋多個欄位

select city,country from table

③同時搜尋兩個表的內容，假設兩個表裡id欄位內容相同

select 
a.city,
a.country, 
b.number
from table1 a
left join table2 b
on a.id=b.id

④以city分組

select 
a.city,
a.country, 
b.number
from table a
from table b
group by city

⑤以city升序排序

select 
a.city,
a.country, 
b.number
from table a
from table b
group by city
order by city

降序

select 
a.city,
a.country, 
b.number
from table a
from table b
group by city
order by city desc

⑥類似資料透視表功能,計算城市數量

select 
a.city,
a.country, 
b.number,count(1) //括號裡面的1代表以第一列為計數標準。
from table a
from table b
group by city
order by city

⑦計算數量的基礎上去重

select 
a.city,
a.country, 
b.number,count(distinct positionId) //distinct 後面跟具有唯一標識，可用來做去重標準
from table a
from table b
group by city
order by city

⑧多維聚合

select
 
 
a.city,
a.country, 
b.number,count(distinct positionId) 
from table a
from table b
group by city,country //group by 新增多個欄位，它將以多維的形式進行資料聚合
order by city

⑨限制條件，數量500以上的城市

select 
a.city,
count(distinct positionId) 
from table a
group by city having count(distinct positionId) >= 500 
order by city

⑩巢狀子查詢

select * from
(select city ,count (distinct positionId) as counts from table
group by city ) as t1 //as 可命名錶名
where counts >=500