Suppose your SQL table contains duplicate rows and you want to remove those duplicate rows. Many times, we face these issues. It is a best practice as well to use the relevant keys, constrains to eliminate the possibility of duplicate rows however if we have duplicate rows already in the ta...
Now we have realized that custid 1, 4 & 5 are duplicate. The self-join statement accompanied by delete statement will give us the desired output of keeping the last duplicate record by eliminating all the previous duplicate records. We will use theCommon Table Expression (CTE)and put the Sel...
Write a SQL query to delete all duplicate email entries in a table namedPerson, keeping only unique emails based on itssmallestId. +---+---+ | Id | Email | +---+---+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +---+---+ Id is the ...
分析select*fromt_table_1wheretask_idin(selectidfromt_table_2whereuid = #{uid}) 回到这条简单sql,包含子查询,按照我们的理解,mysql应该是先执行子查询:select id from t_table_2 where uid = #{uid},然后再执行外部查询:select * from t_table_1 where task_id in,但这不一定,例如我关了这个参数...
SELECT class_num, class_name FROM class WHERE class_num IN (SELECT class_num FROM roster); semijoin有以下几种策略,以下是官方的解释: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...
DELETETFROM (SELECTROW_NUMBER()OVER(PartitionBY[ID],[Name],[Age],[Sex]ORDERBY[ID])ASRowNumber,*FROM#Temp)T WHERET.RowNumber>1 SELECT*FROM#temp URL:http://www.sqlservercentral.com/scripts/duplicate+rows/71078/ Comments Comment: You need tologinto post a comment....
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。
DELETETFROM (SELECTROW_NUMBER()OVER(PartitionBY[ID],[Name],[Age],[Sex]ORDERBY[ID])ASRowNumber,*FROM#Temp)T WHERET.RowNumber>1 SELECT*FROM#temp URL:http://www.sqlservercentral.com/scripts/duplicate+rows/71078/ Comments Comment: You need tologinto post a comment....
开始我们拿sql到数据库查询平台查库执行计划,无奈这个平台有bug,delete语句无法查看,所以我们改成select,“应该”是一样。这个“应该”加了双引号,导致我们走了一点弯路。 EXPLAIN SELECT * from t_table_1 where task_id in (select id from t_table_2 where uid = 1) ...
删除Table中重复的记录 (Delete data for duplicate) 状况是:除了主键不一样外,其余全一样.而不想把数据导出,删掉重复的记录,再重新导入 今天在工作中突然遇到这个问题,记得一二年前也有遇到这种问题,后来解决了. 现在却一时记不起当时的方法.没办法了自己再想吧.最后我用起了这种方法,也算是挺简单的....