如何检索表中的行

Question

表A

columna   
---------
   A
   B            
   C
   :
   :
   Z

以下是如何选择偶数行。我写过像这样的查询

select * from (select row_number()over(order by no asc ) as number   
  from number 
 where mod(number,2)=0)as even 

它不起作用。

Answer 1

尝试

select *  
  from 
(
  select *, row_number() over (order by columna) as rnum   
    from tablea
) q
 where mod(rnum, 2) = 0

输出：

| NO | RNUM |
|----|------|
|  B |    2 |
|  D |    4 |
|  F |    6 |

这是 SQLFiddle 演示

Answer 2

SQL> desc member_list
 Name                            Null?    Type
 ------------------------------- -------- ----
 E_MAIL                                   VARCHAR2(50)
 NAME                                     VARCHAR2(50)


select e_mail from (select rownum row_num, e_mail from member_list)
where mod(row_num,2) = 0 -- EVEN

给你一个例子试试这个

Answer 3

WITH cte AS(
    SELECT *
    ,      ROW_NUMBER()OVER(ORDER BY no)AS RowNum
    FROM number t
)
SELECT cte.* FROM cte
WHERE  mod(RowNum,2) = 0

Answer 4

不知道abt postgres但是在oracle你可以这样做

SELECT * FROM   
    (SELECT columna, ROWNUM RNUM  
            FROM tableA 
            ORDER BY columna)   
    where MOD(RNUM,2)=0