SQL查詢模擬不同

Question

SELECT DISTINCT col1, col2 FROM table t ORDER BY col1; 

這給了我不同的組合col1 & col2。是否有另外一種方法來編寫Oracle SQL查詢來獲得col1 & col2記錄與使用關鍵字distinct的唯一組合？

Answer 1

我不明白爲什麼你會想，但你可以做

SELECT col1, col2 FROM table_t GROUP BY col1, col2 ORDER BY col1 

Answer 2

select col1, col2 
from table 
group by col1, col2 
order by col1 

或不太優雅的方式：

select col1,col2 from table 
UNION 
select col1,col2 from table 
order by col1; 

或更少優雅的方式：

select a.col1, a.col2 
from (select col1, col2 from table 
UNION 
select NULL, NULL) a 
where a.col1 is not null 
order by a.col1 

Answer 3

另 - 但過於複雜，有些沒用 - 解決方案：

select * 
from (
    select col1, 
      col2, 
      row_number() over (partition by col1, col2 order by col1, col2) as rn 
    from the_table 
) 
where rn = 1 
order by col1 

Answer 4

運用獨特的關鍵字這是DISTINCT的同義詞：

SELECT UNIQUE col1, col2 FROM table t ORDER BY col1; 

Answer 5

另一個...

select 
    col1, 
    col2 
from 
    table t1 
where 
    not exists (select * 
       from table t2 
       where t2.col1 = t1.col1 and 
        t2.col2 = t1.col2 and 
        t2.rowid > t1.rowid) 
order by 
    col1; 

Answer 6

上的變化@aF提供的UNION解決方案。 ：

INTERSECT

SELECT col1, col2 FROM tableX 
INTERSECT 
SELECT col1, col2 FROM tableX 
ORDER BY col1; 

MINUS

SELECT col1, col2 FROM tableX 
MINUS 
SELECT col1, col2 FROM tableX WHERE 0 = 1 
ORDER BY col1; 

MINUS（第二版，它會返回一行比其他版本少，如果有(NULL, NULL)組）

SELECT col1, col2 FROM tableX 
MINUS 
SELECT NULL, NULL FROM dual 
ORDER BY col1; 

Answer 7

另一個...

select col1, 
     col2 
from  (
     select col1, 
       col2, 
       rowid, 
       min(rowid) over (partition by col1, col2) min_rowid 
     from table) 
where rowid = min_rowid 
order by col1;