Question

Table A contains multiple records that should be deleted from Table B. However, there can be multiple records in Table B that match a single record in Table A. I only want to delete the first matching record in Table B for each record in Table A. If there are 50 records in Table A then a maximum of 50 records should be deleted from Table B. I’m using the SQL statement below which is deleting more records from Table B than are listed in Table A due to multiple matches. I can not further restrict the matching criteria in my statement due to limitations in the data.

DELETE FROM [#DraftInvoiceRecords] FROM [#DraftInvoiceRecords]
INNER JOIN [#ReversedRecords]
ON [#DraftInvoiceRecords].employee = [#ReversedRecords].employee 
  and [#DraftInvoiceRecords].amount = [#ReversedRecords].amount
  and [#DraftInvoiceRecords].units = [#ReversedRecords].units

Answer 1

You need some way to distinguish the rows to delete from the rows to keep. I’ve used someOtherColumn in the below to achieve this:

create table #DraftInvoiceRecords (
    employee int not null,
    amount int not null,
    units int not null,
    someOtherColumn int not null
)
create table #ReversedRecords (
    employee int not null,
    amount int not null,
    units int not null
)
insert into #DraftInvoiceRecords (employee,amount,units,someOtherColumn)
select 1,1,1,1 union all
select 1,1,1,2
insert into #ReversedRecords (employee,amount,units)
select 1,1,1
delete from dir
from
    #DraftInvoiceRecords dir
        inner join
    #ReversedRecords rr
        on
            dir.employee = rr.employee and
            dir.amount = rr.amount and
            dir.units = rr.units
        left join
    #DraftInvoiceRecords dir_anti
        on
            dir.employee = dir_anti.employee and
            dir.amount = dir_anti.amount and
            dir.units = dir_anti.units and
            dir.someOtherColumn > dir_anti.someOtherColumn --It's this condition here that allows us to distinguish the rows
where
    dir_anti.employee is null

select * from #DraftInvoiceRecords

drop table #DraftInvoiceRecords
drop table #ReversedRecords