DELETE FROM table_name WHERE column_name IN ( SELECT column_name FROM table_name GROUP BY column_name HAVING COUNT(*) > 1 ); 方法三:使用ROW_NUMBER()函数 可以使用ROW_NUMBER()函数给每条记录赋予一个唯一的行号,然后根据行号来删除重复的记录。
我们以person表为例,假设我们要去除重复的name字段: WITHCTEAS(SELECTname,ROW_NUMBER()OVER(PARTITIONBYnameORDERBY(SELECTNULL))ASrow_numFROMperson)DELETEFROMCTEWHERErow_num>1; 1. 2. 3. 4. 5. 6. 7. 8. 此段代码会根据name字段对每一组进行分区并赋值行号,最后删除行号大于 1 的记录,完成去重。 ...
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 * from t_table_1 where task_id in (select id from t_table_2 where uid = #{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,...
(query); // 消除select从句后的冗余列 removeUnneededColumnsFromSelectClause(select_query, required_result_columns, remove_duplicates); // 执行标量子查询,并且用常量替代标量子查询结果 executeScalarSubqueries(query, context, subquery_depth); // 如果是select语句还会做下列优化: // 谓词下移优化 Predicate...
Remove Duplicates from Sorted Array 题目大意对排好序的list去重,输出去重后长度,并且不能创建新的数组解题思路快慢指针代码官方答案数组完成排序后,我们可以放置两个指针...只要 nums[i] = nums[j]nums[i]=nums[j],我们就增加 jj 以跳过重...
select * from customers1 go We want remove one of the duplicate records of John. By issuing the following summary query, we can see which see which records are duplicate. select * from customers1 Group by Custid,CustName, CustCity, Passport_Number Having count(*) > 1 ...
)WITH(...);--remove duplicate rows on order_id and keep the first occurrence row,--because there shouldn't be two orders with the same order_id.SELECTorder_id,user, product, numFROM(SELECT*, ROW_NUMBER()OVER(PARTITIONBYorder_idORDERBYproctimeASC)ASrow_numFROMOrders)WHERErow_num=1 ...
These five rows are combined with the results of the first SELECT by using the UNION ALL keywords. This example doesn't remove the duplicates between the two sets of five rows. The final result has 10 rows. SQL Copy USE AdventureWorks2022; GO IF OBJECT_ID('dbo.EmployeeOne', 'U') IS...
allow the user to select the destination folder for file download? allowing a textbox to only enter date alternative to session variable An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed...