Question

我找到了以下删除重复项的方法：

DELETE FROM
   table_name A
WHERE
  a.rowid >
   ANY (
     SELECT
        B.rowid
     FROM
        table_name B
     WHERE
        A.col1 = B.col1
     AND
        A.col2 = B.col2
        );

有人可以一步一步地解释我的查询是如何工作的吗？

TIA！

Answer 1

像这样：

DELETE FROM         // The command to delete
   table_name A     //the table in which you want to remove duplicate
WHERE               //condition
  a.rowid >         //checking the rowid which oracle adds to each row. Oracle Database rowid values contain information necessary to locate a row.
   ANY (             //any row which has a condition
     SELECT          //select
        B.rowid      //rowid
     FROM             //from  
        table_name B    //table name with alias name as B. Is used for making a self join
     WHERE               //condition
        A.col1 = B.col1    //where the column1 has the same rowid 
     AND                    //and
        A.col2 = B.col2     //where the column2 has the same rowid 
        );

Answer 2

在Oracle中，ROWID是一个伪列，指向一行的物理位置。该查询执行自连接并获取具有相同值的第1列和第1列的那些行。第2列 - 假设这些密钥足以识别为重复行。

一旦获取了行，查询就会删除那些大于第一行读取的rowid，从而删除重复项

Oracle - 删除重复项

2 个答案: