remove duplicate rows in sql

server| Repeat | Recurring nightmare for Developers--delete duplicate records Presumably every developer has had a similar experience, and when querying or counting the database, the query and statistic results are inaccurate due to duplicate records in the table. The solution to this problem is to delete the duplicate records and keep only one of them. In

SQL removes duplicate records, SQL removes duplicates There are two Repeated Records. One is a completely repeated record, that is, records with all fields being repeated, and the other is records with duplicate key fields, such as duplicate Name fields, other fields are not

There are many ways to delete duplicate records. Here I summarize a variety of SQL statements for deleting restart records, such as deleting duplicate id data and searching for duplicate records, remove the smallest record, delete the repeat record, retain only one record an

SQL statement for data duplication between Oracle and MySQL It can be said that this data is repeated, no matter in development, data maintenance and experience interviews, you should encounter common problems! Here, I also paid special attention to some articles on the Internet and collected them for your reference and study. It also facilitates your future review! Repeated data processing in Oracle How to query

table tmp_wrap;Query OK, 0 rows affected (0.05 sec) 2. There is also a very streamlined approach. Find the duplicate and remove the smallest one. The Code is as follows: Delete users_groups as a from users_groups as,(Select *, min (id) from users_groups group by uid having count (1)> 1) As BWhere a. uid = B. uid and a. id> B. id;

,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)and rowID not in (select min (rowid) from Vitae GROUP by PEOPLEID,SEQ have Count (*) >1)5. Find redundant duplicate records (multiple fields) in the table, not including the smallest ROWID recordsSELECT * from Vitae awhere (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)and rowID not in (select min (rowid) from Vitae GROUP by PEOPLEID,SEQ have Count

full-volume scan operation. You should find an alternative or use a precondition statement to minimize the number of rows before the like lookup.B, try to avoid the large table data for select top n * from XXX where xxxx order BYNEWID () takes a random record of the operation. The NEWID () operation reads the full amount of data and then sorts it. Also consumes a lot of CPU and read operations. Consider using the rand () function, which I'm still wor

Tags: title max repeat record ROWID delete ROM using statement casehttp://blog.csdn.net/anya/article/details/6407280/With SQL statements, delete duplicates only keep one In thousands of records, there are some same records, how can you use SQL statements, delete duplicates1, look for redundant records in the table, duplicate records are based on

the retrieval of rows from a table or view.It contains keys that are generated by one or more columns in a table or view. These keys are stored in a structure (B-tree), allowing SQL Server to quickly and efficiently find the rows associated with the key value.7. Type of index: clustered, non-clustered.There is also a unique index, a unique index that ensures tha

Then I thought about a statement: The Code is as follows: Mysql> use mysqlDatabase changedMysql> select * from duplicate;+ ---- + ------- +| Id | name |+ ---- + ------- +| 1 | wang || 3 | wdang || 5 | wdand || 6 | wddda || 2 | wang || 4 | wdang |+ ---- + ------- +6 rows in set (0.00 sec)Mysql> delete duplicate as a from

also a very streamlined approach. Look for duplicates and get rid of the smallest one. The code is as follows Copy Code Delete Users_groups as a from users_groups as a,(Select *,min (ID) from Users_groups GROUP by UID has count (1) > 1) as Bwhere A.uid = B.uid and a.id > b.id;(7 row (s) affected)(0 ms taken)Query result (7 records)ID UID GID1 11 5022 107 5023 100 5034 110 5015 112 5016 104 5029 102 501 3. Now look at the efficiency of these two approaches

sec) Mysql> Delete Duplicate as a from duplicate as a, -> ( -> SELECT * from duplicate group by name has count (1) >1) as B nb sp;-> where a.name=b.name and a.id > b.id; Query OK, 2 rows Affected (0.00 sec) Mysql> select * FROM duplicate +----+-------+ | id | name |

The question of how to dynamically number rows in SQL, plus line numbers, is a classic problem in database queries. I'll sort out the present method and share the skills. The code is based on the pubs boilerplate database. In SQL, these two methods are generally: 1. Use of temporary tables You can use SELECT into to create a temporary table, in the first column

SQL Server converts rows to columns: for example, if a table contains only a small amount of data, you can use static SQL statements such as selectstuName and max (caseCoursewhen language thenscoreelse0end) as language, max (caseCoursewhen math thenscoreelse0end) as math, max (caseCoursewhen SQL Server transfers

#T a where exists (select 1 from #T where Num=a.num and Name=a.name and id>a.id)--keep only one recordGoALTER TABLE #T drop column id--Delete identity column--View ResultsSELECT * FROM #T/*Num Name----------- ----1 A2 B(2 rows affected)*/--use Method 3 after re-executing test dataMethod 3:Declare roy_cursor Cursor Local forSelect COUNT (1) -1,num,name from #T GROUP by Num,name have count (1) >1declare @con int, @Num int, @Name nvarchar (1)Open Roy_cu

, 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

With SQL statements, deleting repeated items only keeps one record in thousands of records, and some identical records exist. How can I use SQL statements, delete duplicate records 1. Search for redundant duplicate records in the Table. duplicate records are used to determin

Deleting duplicate rows on SQL Server is one of the most common operations. The following describes six methods that can be used to delete duplicate rows on SQL Server for your reference. 1. If an ID field exists, it is a unique f

Each time you import an Excel table to the database, several more rows are displayed as 'null' rows. The following prompt is displayed when you delete the table. "The key column information is insufficient or incorrect. Update affects multiple rows! " Solution: You can see from your description that you have imported data from Excel to