how to find duplicate rows in sql

with SQL statements, delete duplicates only keep oneThe addition of the HAVING clause in SQL is because the WHERE keyword cannot be used with the aggregate function. All of the aggregate functions are shown in the following table:MINReturns the smallest value in a given columnMAXReturns the largest value in a given columnSUMReturns the sum of all the values in a given columnAvgReturns the average of all the

In this example, we will use the following table, which has duplicate PK values. In this table, the primary key is two columns (col1 and col2 ). We cannot create a unique index or primary key constraint because the two rows have duplicate primary keys. This process demonstrates how to identify and delete duplicate prim

Label:https://leetcode.com/problems/delete-duplicate-emails/Delete Duplicate EmailsWrite a SQL query to delete all duplicate e-mail entries in a table named Person , keeping unique emails based on its smallest Id. +----+------------------+ | Id | Email | +----+------------------+ | 1 | [Email p

When the SQL statement deletes duplicate records and there is no size relationship between them, it processes repeated values. When the SQL statement deletes duplicate records and there is no size relationship between them, it processes repeated values. When the SQL state

, COL2 after grouping COL1, COL2 content and the number of records in each group.if: SELECT COL1, COL2, COUNT (DISTINCT COL3) as Expr1From MyTestGROUP by COL1, COL2The result is:COL1 COL2 COUNT1 A 12 A 12 B 13 B 14 C 1If the 7th record is changed to 7 4 c cThe result is:COL1 COL2 COUNT1 A 12 A 12 B 13 B 14 C 2That is, press COL1, COL2 after grouping COL1, the contents of COL2 and the number of records in each group COL3 not repeating.Using DISTINCT to eliminate duplicatesThe DISTINCT keyword can

SQL Multiple primary key tables, when the inserted data is duplicated, are prompted to violate the primary KEY constraint that cannot be inserted by the error. So, how do I find duplicate values for the inserted data? Workaround: Use Group bySuppose there is a table #a , there are saleid,vendorid,comid,price,saleprice,quantity and other fields. The primary key is: Saleid,vendorid,comid three of them. Assu

a. Customer No.> = B. Customer No. Group by A. Customer No., B. company name order by no;2. SQL Server 2005 constructs the sequence number column Method 1:Select rank () over (order by customer No. DESC) as No., customer No., company name from customer; Method 2:With table(Select row_number () over (order by customer No. DESC) as No., customer No., company name from customer)Select * from tableWhere no. Between 1 and 3; 3. rowid in Oracle can also

The table structure is created like the following code Copy Code code as follows: CREATE TABLE TEST_TB ( TestID int NOT null identity (1,1) primary key, Caption nvarchar (MB) null ); Go Solution 1: The first idea for this question may be: Is it OK to add a unique key to the caption field? OK, let's follow this thread and create a unique index first. Copy Code code as follows: CREATE UNIQUE nonclustered INDEX UN_TEST_TB On TEST_TB (Caption) Go

2601, Level 14, State 1, line 1thYou cannot insert a row of duplicate keys in an object ' DBO.TEST_TB ' with a unique index ' UN_TEST_TB '.The statement was terminated. So the solution is not going to work. Solution 2: Add a constraint so that SQL server, when inserting data, verifies that there is a value in the existing data that is now being inserted. Since this constraint is not a simple

Business requirementsRecently made a small tool for the company to bring data from one database (data source) into another (target database). The data required to import the target database cannot be duplicated. But the situation is that the data source itself has duplicate data. So you need to clear the data source data first.So we summarize the query and processing of the duplicate data. This is only a da

Merge duplicate rows of data into one row in SQL, concatenate the content of multiple fieldname fields, and separate them with commas. Next we will introduce the detailed implementation of SQL statements for you. Merge duplicate rows