Ret DB-duplikerede poster (MySQL-fejl)

Sådan angiver du alle uregelmæssighederne:

SELECT name, count(*) FROM TableA GROUP BY name HAVING count(*) > 1;

Der er et par måder at tackle sletning af dups, og din vej vil afhænge meget af antallet af dups du har.

Se dette SÅ spørgsmål til måder at fjerne dem fra dit bord.

Her er den løsning, jeg gav der:

-- Setup for example
create table people (fname varchar(10), lname varchar(10));

insert into people values ('Bob', 'Newhart');
insert into people values ('Bob', 'Newhart');
insert into people values ('Bill', 'Cosby');
insert into people values ('Jim', 'Gaffigan');
insert into people values ('Jim', 'Gaffigan');
insert into people values ('Adam', 'Sandler');

-- Show table with duplicates
select * from people;

-- Create table with one version of each duplicate record
create table dups as 
    select distinct fname, lname, count(*) 
    from people group by fname, lname 
    having count(*) > 1;

-- Delete all matching duplicate records
delete people from people inner join dups 
on people.fname = dups.fname AND 
   people.lname = dups.lname;

-- Insert single record of each dup back into table
insert into people select fname, lname from dups;

-- Show Fixed table
select * from people;