Question

oracle 查询数据只要排序后的第一条记录（不用rownum=1），sql语句怎么写

SELECT field1, field2, field3... fieldn
FROM (SELECT field1, field2, field3...fieldn, ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK ) FROM tab ) t
WHERE rk = 1
把这个语句嵌套到别的语句里面后
select t.a,t.b,
(SELECT field1, field2, field3... fieldn
FROM (SELECT field1, field2, field3...fieldn, ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK ) FROM tab where field1=t.a) t
WHERE rk = 1)
from lkk t;
会报错 ora-00904 where field1=t.a) "T"."A"请教高手怎么改

Answer 1

1、创建测试表，

create table test_order(id number, value varchar2(50));

2、插入测试数据

insert into test_order values(3,'v3');

insert into test_order values(2,'v2');

insert into test_order values(1,'v1');

insert into test_order values(5,'v5');

insert into test_order values(4,'v4');

commit;

3、查询表中全量数据，可以发现数据并未排序，select t.*, rowid from test_order t;

4、编写sql，数据只要排序后的第一条记录（不用rownum=1） select * from (select t.*, row_number() over(order by id) rn from test_order t) t where rn = 1;

Answer 2

假设排序的字段名字为field1降序, table name: tab
SELECT field1, field2, field3... fieldn
FROM (SELECT field1, field2, field3...fieldn, ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK ) FROM tab ) t
WHERE rk = 1

00904是说列名不正确，仔细看了下，AS RK后面多了一个括号，下面这样就可以了
SELECT field1, field2, field3... fieldn
FROM (SELECT field1, field2, field3...fieldn,
ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK
FROM tab
where field1=表名.字段名) t
WHERE rk = 1

我给你改一下吧，你写的那个效率很低的
SELECT t1.a, t1.b, t2.field1, t2.field2, t2.field3...t2.fieldn
FROM lkk t1,
(SELECT field1, field2, field3...fieldn,
ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK
FROM tab) t
WHERE t.field1 = t1.a
AND t.rk = 1

Answer 3

首先在 XSREMOBILE 表上建 SENDDATE和ID 的复合索引.

把 WHERE ROWNUM < 50 + 1
改为 WHERE ROWNUM <= 50

应该可以快些.

SELECT /*+ FIRST_ROWS */ *
FROM (SELECT /*+ parallel(M,10) */ *
FROM XSREMOBILE M
WHERE M.SENDDATE >= 20101126
AND M.SENDDATE <= 20101126
oRDER BY M.ID DESC
)
WHERE ROWNUM <= 50

Answer 4

SELECT field1, field2, field3... fieldn
FROM (SELECT field1, field2, field3...fieldn, ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK ) FROM tab ) t
WHERE rk = 1
把这个语句嵌套到别的语句里面后
select t.a,t.b,
(SELECT field1, field2, field3... fieldn
FROM (SELECT field1, field2, field3...fieldn, ROW_NUMBER() OVER(ORDER BY field1 DESC) AS RK ) FROM tab where field1=t.a) t
WHERE rk = 1)
from lkk t;
会报错 ora-00904 where field1=t.a)

Answer 5

如果该表有时间或数值类型字段的话可以采用如下；

SELECT * 

            FROM table a 

            WHERE a.time = (SELECT MAX (b.time) 

                                          FROM table b) ;