sql - 模拟不同的 SQL 查询

Question

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

这给了我独特的col1&组合col2。是否有另一种编写 Oracle SQL 查询的方法来获得col1&col2记录的唯一组合，而不使用关键字 distinct？

Answer 1

使用作为 DISTINCT 同义词的 UNIQUE 关键字：

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

Answer 2

我不明白你为什么想要，但你可以做到

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

Answer 3

Yet another ...

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 4

另一个 - 但过于复杂且有点无用 - 解决方案：

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 5

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

或更不优雅的方式：

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

或者更不优雅的方式：

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 6

UNION@aF 解决方案的变体。：

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（第二个版本，如果有组，它会比其他版本少返回一行(NULL, NULL)）

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

Answer 7

其他 ...

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;