And that’s how we can delete duplicate records in SQL Server with tables without primary key, containing primary key and by keeping one original row. 原文链接:http://www.codesec.net/view/449563.html
The execution should happen where the data is for best efficiency which is possible with SQL window functions: The rows are partitioned by the columns indicating a duplicate row. For every combination of the specified columns a partition is automatically created to collect the duplicate rows. ...
All rows in Oracle have a rowid. This is a physical locator. That is, it states where on disk Oracle stores the row. This unique to each row. So you can use this value to identify and remove copies. To do this, replace min() with min(rowid) in the uncorrelated delete: Copy code ...
WHERE T.RowNumber > 1); Check the result: 1 2 3 4 5 6 7 8 9 SELECT *FROM tbl_RemoveDuplicate; id | name ---+--- 1 | ABC 2 | XYZ 4 | RFQ 5 | PQR 6 | EFG (5 rows) SQL Puzzle: SQL Advance Query - Find the Order basis on thier Status and Step Comments...
If we look at the result set, we can easily understand thatBookNumber: 3andBookNumber: 4are duplicate rows. Previously, it was explained in detailhow to remove duplicates in SQL. We must delete them to keep the database consistent.
sql简写一下就是 select*fromt_table_1 t1whereexists(selectt2.idfromt_table_2 t2wheret2.uid=1andt1.task_id=t2.id) 可以看到in可以改成semijoin或exists,最终优化器选择了exists,因为我们关闭了semijoin开关。 按照这条sql逻辑查询,将会遍历t_table_1表的每一行,然后代入子查询看是否匹配,当t_table_...
Duplicate Weedout: Run the semijoin as if it was a join and remove duplicate records using a temporary table. FirstMatch: When scanning the inner tables for row combinations and there are multiple instances of a given value group, choose one rather than returning them all. This "shortcuts" ...
DELETEFROMusersWHEREemailIN(SELECTemailFROM(SELECTemail,COUNT(*)FROMusersGROUPBYemailHAVINGCOUNT(*)>1)ASduplicate_emails); 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 以上的SQL语句中,我们首先使用子查询找出重复的email,然后在外层的DELETE语句中使用WHERE子句来指定要删除的记录。
Duplicate Weedout: Run the semijoinasifit was ajoinandremove duplicate recordsusinga temporary table.FirstMatch:Whenscanning the inner tablesforrow combinationsandthere are multiple instancesofa given valuegroup, choose one rather than returning them all. This"shortcuts"scanningandeliminates productionofunn...
I have 2 columns name and Score. I would like to delete duplicate rows for each category(Name).For instance- i would like to see one of the Scores(2) to be...