oracle怎么进行数据去重

去重方法：1、利用distinct关键字去重，语法“SELECT DISTINCT 字段名 FROM 表名;”；2、利用窗口函数row_number () over()去重；3、利用“group by”子句去重，语法“select 字段名 from 表名 group by 字段名;”；4、利用rowid进行伪列去重。

本教程操作环境：Windows7系统、Oracle 11g版、Dell G3电脑。

业务场景

需要查询某数据，由于需要三张表关联查询，查询结果如下：

原始SQL语句

SELECT 
  D.ORDER_NUM AS "申请单号" ,
  D.CREATE_TIME ,
  D.EMP_NAME AS "申请人",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_wasteName')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "废料名称",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_units')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "单位",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_estimate')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "预估数量",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_stockRemoval')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "累计出库数量",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_receivingTime')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdCGYTX'
  ) AS "收购方收货时间",
  (SELECT extractvalue(t2.row_data,'/root/row/FI13_collectionTime')
  FROM dat_table_row t2
  WHERE d.document_id = t2.document_id
  AND t2.table_id     = 'dynamicRowsIdPTSJSKSJ'
  ) AS "实际收款时间"
FROM dat_document d,
  dat_table_row dtr
WHERE d.form_name       ='FI14'
AND d.document_id       =dtr.document_id
AND (D.DOCUMENT_STATUS != 'deleted'
OR D.DOCUMENT_STATUS   IS NULL )
  --AND TO_CHAR(d.create_time,'yyyy-MM-dd') BETWEEN '2020-01-01' AND '2021-03-26'
AND d.order_num = 'FI1420210708002' --FI1420210708002
ORDER BY d.CREATE_TIME DESC;

方法1：distinct去重

SELECT DISTINCT可以用来过滤结果集中的重复行，确保SELECT子句中返回指定的一列或多列的值是唯一的。

DISTINCT语句的语法如下：

SELECT DISTINCT column_1,
    column_2,
        ...
        FROM
    table_name;

示例：

SELECT 
  D.ORDER_NUM AS "申请单号" ,
  D.CREATE_TIME ,
  D.EMP_NAME AS "申请人",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_wasteName')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "废料名称",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_units')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "单位",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_estimate')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "预估数量",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_stockRemoval')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) AS "累计出库数量",
  (SELECT extractvalue(t1.row_data,'/root/row/FI13_receivingTime')
  FROM dat_table_row t1
  WHERE d.document_id = t1.document_id
  AND t1.table_id     = 'dynamicRowsIdCGYTX'
  ) AS "收购方收货时间",
  (SELECT extractvalue(t2.row_data,'/root/row/FI13_collectionTime')
  FROM dat_table_row t2
  WHERE d.document_id = t2.document_id
  AND t2.table_id     = 'dynamicRowsIdPTSJSKSJ'
  ) AS "实际收款时间"
FROM dat_document d,
  dat_table_row dtr
WHERE d.form_name       ='FI14'
AND d.document_id       =dtr.document_id
AND (D.DOCUMENT_STATUS != 'deleted'
OR D.DOCUMENT_STATUS   IS NULL )
  --AND TO_CHAR(d.create_time,'yyyy-MM-dd') BETWEEN '2020-01-01' AND '2021-03-26'
AND d.order_num = 'FI1420210708002' --FI1420210708002
ORDER BY d.CREATE_TIME DESC;

注意：DISTINCT后面要跟ORDER BY的字段，Oracle先执行 DISTINCT去重后，再使用ORDER BY进行排序的。所以如果在ORDER BY需要排序的字段，没有在 distinct 后的字段中，自然会抛错。

报错信息如下：

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方法2：row_number() over()

语法格式

select * from
(select A.*, row_number() over(partition by A.name1 order by A.name12 desc) rn from A)
where rn = 1

示例

select * from (
select 
  d.order_num as "申请单号" ,
  d.create_time ,
  d.emp_name as "申请人",
  (select extractvalue(t1.row_data,'/root/row/FI13_wasteName')
  from dat_table_row t1
  where d.document_id = t1.document_id
  and t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) as "废料名称",
  (select extractvalue(t1.row_data,'/root/row/FI13_units')
  from dat_table_row t1
  where d.document_id = t1.document_id
  and t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) as "单位",
  (select extractvalue(t1.row_data,'/root/row/FI13_estimate')
  from dat_table_row t1
  where d.document_id = t1.document_id
  and t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) as "预估数量",
  (select extractvalue(t1.row_data,'/root/row/FI13_stockRemoval')
  from dat_table_row t1
  where d.document_id = t1.document_id
  and t1.table_id     = 'dynamicRowsIdPTFLXX'
  ) as "累计出库数量",
  (select extractvalue(t1.row_data,'/root/row/FI13_receivingTime')
  from dat_table_row t1
  where d.document_id = t1.document_id
  and t1.table_id     = 'dynamicRowsIdCGYTX'
  ) as "收购方收货时间",
  (select extractvalue(t2.row_data,'/root/row/FI13_collectionTime')
  from dat_table_row t2
  where d.document_id = t2.document_id
  and t2.table_id     = 'dynamicRowsIdPTSJSKSJ'
  ) as "实际收款时间",
  row_number() over(partition by d.order_num  order by d.create_time desc) rn 
from dat_document d,
  dat_table_row dtr
where d.form_name       ='FI14'
and d.document_id       =dtr.document_id
and (d.document_status != 'deleted'
or d.document_status   is null )
  --AND TO_CHAR(d.create_time,'yyyy-MM-dd') BETWEEN '2020-01-01' AND '2021-03-26'
and d.order_num = 'FI1420210708002' --FI1420210708002
) where rn = 1;

查询结果

方法3：group by 

select 字段名 from 表名
group by 字段名;

方法4：利用rowid（伪列去重）

select id,name,age from test t1
where t1.rowid in (select min(rowid) from test t2 where t1.name=t2.name and t1.age=t2.age);

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