mysql 查詢中的 1:N 實現

Question

假設表state_info 2 列。

state       |  district
------------+---------------
Karnataka   |  Bangalore
Karnataka   |  Belgium
Karnataka   |  Mysore
Mumbai      |  Sandra
Mumbai      |  Madeira

我想在單列中輸出它們

Karnataka
Bangalore
Belgium
Mysore

Mumbai
Sandra
Madeira

狀態低於其 dist ，再次狀態低於其 dist

Answer 1

用

SELECT CONCAT(state, ', ', district) FROM state_info;

要得到

Karnataka, Bangalore
Karnataka, Belgium
Karnataka, Mysore
Mumbai, Sandra
Mumbai, Madeira

Answer 2

你可以這樣做

Select Distinct(state) from Table1
UNION 
Select Distinct(district) from Table1;

結果將是

Bangalore
Belgium
Mysore
Sandra
Madeira
Karnataka
Mumbai

Answer 3

select * from (
 Select Distinct(state) as data from Table1
 UNION 
 Select Distinct(district) as data from Table1;
) order by  data