如何在Oracle中的表中找到重复值？

Question

什么是最简单的SQL语句,它将返回给定列的重复值及其在Oracle数据库表中的出现次数？

例如:我有一个JOBS包含列的表JOB_NUMBER.我怎样才能知道我是否有任何副本JOB_NUMBER,以及它们被复制了多少次？

Answer 1

SELECT column_name, COUNT(column_name)
FROM table_name
GROUP BY column_name
HAVING COUNT(column_name) > 1;

Answer 2

其他方式:

SELECT *
FROM TABLE A
WHERE EXISTS (
  SELECT 1 FROM TABLE
  WHERE COLUMN_NAME = A.COLUMN_NAME
  AND ROWID < A.ROWID
)

当有索引时,工作正常(足够快)column_name.并且它是删除或更新重复行的更好方法.

Answer 3

最简单的我能想到:

select job_number, count(*)
from jobs
group by job_number
having count(*) > 1;

Answer 4

如果您不需要知道重复的实际数量,则不需要在返回的列中包含计数.例如

SELECT column_name
FROM table
GROUP BY column_name
HAVING COUNT(*) > 1

Answer 5

怎么样:

SELECT <column>, count(*)
FROM <table>
GROUP BY <column> HAVING COUNT(*) > 1;

要回答上面的例子,它看起来像:

SELECT job_number, count(*)
FROM jobs
GROUP BY job_number HAVING COUNT(*) > 1;

Answer 6

如果多列标识唯一行(例如关系表),您可以使用以下内容

使用行id例如emp_dept(empid,deptid,startdate,enddate)假设empid和deptid是唯一的并且在那种情况下标识行

select oed.empid, count(oed.empid) 
from emp_dept oed 
where exists ( select * 
               from  emp_dept ied 
                where oed.rowid <> ied.rowid and 
                       ied.empid = oed.empid and 
                      ied.deptid = oed.deptid )  
        group by oed.empid having count(oed.empid) > 1 order by count(oed.empid);

如果这样的表有主键,那么使用主键而不是rowid,例如id是pk然后

select oed.empid, count(oed.empid) 
from emp_dept oed 
where exists ( select * 
               from  emp_dept ied 
                where oed.id <> ied.id and 
                       ied.empid = oed.empid and 
                      ied.deptid = oed.deptid )  
        group by oed.empid having count(oed.empid) > 1 order by count(oed.empid);

Answer 7

我通常使用Oracle 分析函数ROW_NUMBER()。

c1假设您要检查关于基于列 ( 、c2、 )构建的唯一索引或主键的重复项c3。然后你将这样走，调出ROWIDs 行，其中所带来的行数ROW_NUMBER()为>1：

Select *
From Table_With_Duplicates
Where Rowid In (Select Rowid
                  From (Select ROW_NUMBER() Over (
                                 Partition By c1, c2, c3
                                 Order By c1, c2, c3
                               ) nbLines
                          From Table_With_Duplicates) t2
                 Where nbLines > 1)