Scenario 2.a: Delete Duplicate rows but keep one using CTE We need to use the technique of Self Join initially to check for duplicate records containing different custid but same passport number. select distinct a.* from customers2 a join customers2 b on a.custid <> b.custid and a.CustN...
你可以使用 GROUP BY 对重复行进行分组,然后使用 HAVING 子句过滤出重复的行,最后使用 DELETE 语句删除这些行。 sql -- 确定重复行 WITH DuplicateRows AS ( SELECT column1, column2, ..., COUNT(*) FROM original_table GROUP BY column1, column2, ... HAVING COUNT(*) > 1 ) -- 删除重复行 ...
(1, 101), (1, 101), (2, 102); -- 删除重复行 WITH DuplicateRows AS ( SELECT *, ROW_NUMBER() OVER (PARTITION BY StudentID, CourseID ORDER BY (SELECT NULL)) AS RowNum FROM StudentCourses ) DELETE FROM StudentCourses WHERE StudentID IN (SELECT StudentID FROM DuplicateRows...
How to Delete the Duplicate Rows Delete key1by Büşra ÖZCOŞKUNCC BY-SA 4.0 Now you've identified the copies, you often want to delete the extra rows. For simplicity, I'm going to assume that either the rows are exact copies or you don't care which you remove. If there is on...
How to Delete Duplicate Records in Sql Server, removing duplicates using cte, delete duplicate rows from a table in sql SERVER using a CTE.
Delete where BookNumber is 3 and 4. Let us choose the first option. However, remember that it is only valid if there are no rows after the duplicate rows we are aware of. Execute the following script: -- Delete all the data (rows) from the table Book where BookNumber is greater than...
以Duplicate Weedout为例,mysql会先将roster的记录以class_num为主键添加到一张临时表,达到去重的目的。接着扫描临时表,每行去匹配外层表,满足条件则放到结果集,最终返回。具体使用哪种策略是优化器根据具体情况分析得出的,可以从explain的extra字段看到。 那么为什么delete没有使用semijoin优化呢?这其实是mysql的一个bu...
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。 EXPLAINSELECT*fromt_table_1wheretask_idin(selectidfromt_table_2whereuid=1)
SELECTDISTINCT*INTOduplicate_tableFROMoriginal_tableGROUPBYkey_valueHAVINGCOUNT(key_value) >1DELETEoriginal_tableWHEREkey_valueIN(SELECTkey_valueFROMduplicate_table)INSERToriginal_tableSELECT*FROMduplicate_tableDROPTABLEduplicate_table 此脚本按给定顺序执行以下操作: ...
ROW_NUMBER() OVER(PARTITION BY transaction_id ORDER BY transaction_id) AS Duplicate_row FROM Transaction__Table WITH CTE AS (SELECT *, ROW_NUMBER() OVER(PARTITION BY transaction_id ORDER BY transaction_id) AS Duplicate_rows FROM Transaction__Table) DELETE FROM CTE WHERE Duplicate_rows >1; ...