how to eliminate duplicate records in sql

Oracle databases contain many duplicate items because they do not have any constraints. The question now is how to delete these repeated items. Repeat records only keep one of them. The following table creation statement: CREATETABLEmessage_s Oracle databases contain many duplicate items because they do not have any constraints. The question now is how to delete

Query and delete duplicate records of SQL statement 1, find redundant records in the table, duplicate records are based on a single field (ID) to determine the select * from table where Id in (the Select ID from table group Byid h

Unique query for a single table: distinct unique query for multiple tables: When groupbydistinct is used to query multiple tables, leftjoin is still valid and full join is invalid. when mysql is used, sometimes you need to query records that do not repeat a field. Although mysql provides the distinct keyword to filter out redundant duplicate records, only one rec

should be the most effective filtration condition, so the subquery is better than exists, because it is quicker to find out all the orders for the bat and then check if the sales occurred in the last six months. If the table OrderDetail artid field is indexed, this method will be faster, otherwise, this clever action will be eclipsed.Whenever a large number of records are checked for existence, choose in or exists to be considered.For most

updates a row of records or updates all the rows that need to be updated. This problem has plagued me for a long time, in fact, using the values () function all the problems are solved. For example, field A is defined as unique, and records (2,2,9) and (3,2,1) already exist in the original database tables table, and if a value of the inserted record repeats with the original record, the original record is

Oracle databases contain many duplicate items because they do not have any constraints. The question now is how to delete these repeated items. Repeat records only keep one of them. The following table creation statement Create table message_student3 ( Stu_id integer not null, -- the table has no uniqueness constraint. Stu_number varchar (30 ), Stu_name VARCHAR (10) not null, Stu_age NUMBER (2) NOT NULL );

it? "At that time, because it was a very simple question, it was directly completed using SQL statements. The interviewer said that there was a problem. I was wrong when I came back to study it. Now I will share the steps of the study. Study conditions: Window7 + no-install mysql 1. How to delete records with the same attributes except the primary key Main Idea: first, identify non-

Tags: create repeat publish record LIS blog time ROM spanDelete duplicate records in a table, leaving only one entry: Delete from where inch (Select* from,selectmaxfromgroup by having Count > 1 as B); Instance:2. When you want to create a unique index for a table, you need to delete duplicate records because there

ROWIDSql>deletefrom person where rowid not in (select min (rowid) from person Group by email);Method Four: Self-joinSql>delete from person P1 where rowid not in (select min (rowid) from person P2 where p1.email=p2.email);Method Five: Use Row_number ()SQL > Delete from person where rowid in (select Rid from (select rowID rids, Row_number () over (partition by email order by email) (Row_num from person) where row_num>1);Method Six: Use Dense_rank ()De

records or updates all the rows that need to be updated. This problem has plagued me for a long time, in fact, using the values () function all the problems are solved. For example, field A is defined as unique, and records (2,2,9) and (3,2,1) already exist in the original database tables table, and if a value of the inserted record repeats with the original record, the original record is updated, or the