how to delete duplicates from a database table based on a certain field

Question

i have a table that somehow got duplicated. i basically want to delete all records that are duplicates, which is defined by a field in my table called SourceId. There shou

Answer 1

Assuming you have a column ID that can tie-break the duplicate sourceid's, you can use this. Using min(id) causes it to keep just the min(id) per sourceid batch.

delete from tbl
where id NOT in
(
select  min(id)
from tbl
group by sourceid
)

Answer 2

delete from table
where pk in (
select i2.pk
from table i1
  inner join table i2
   on i1.SourceId = i2.SourceId
)

good practice is to start with select * from … and only later replace to delete from …