How to delete records without a primary key in a stardard way (i.e. not using ctid) Case of use

We have a log table without a PK with two columns (date, event); 

You inserted a row. Then you want to undo the inserted record.

Is there a way to delete that row (without deleting other rows with the same data), that doesn't use postgres only capabilities? 

I want a solution that works in another database (it doesn't need to be totally standard, it can be only in just one database: SqLite, Oracle, MySql or SQLServer). 

Example:

create table the_log(
  date date,
  event_id integer
);

insert into the_log(date, event_id) values ('2019-09-21',1),('2019-09-21',1);

select * from the_log;


My atempts:

delete from the_log where row_number() over ()=1;

delete from the_log limit 1;

with the_log_2 as (select *, row_number() over () as version from prueba_sin_clave)
delete from the_log_2 where version=1;


I supouse that the answer is No. I want to know if I am wrong or in what documentation I read that I am right.
CAUTION : This can make you lose data, so consider using transaction block. 

I think this is the more generic solution: 

If you consider that the line you want to delete is:

select * from the_log limit 1 


then if you have one column that has a unique value... 

delete from the_log  
where unique_the_log_column in 
(select unique_log_column from the_log limit 1); 


If you do not have a unique column, but you have two columns that combined generates a unique value:  

delete from the_log  
where (col1, col2) in (select col1, col2 from the_log limit 1); 


Where any_the_log_column is a column with a unique value in this table. 

This will probably delete the first line of the log table in any dbms - if data in column is not repeated, but remember that tables sometimes is not selected ordered in some databases so you must have a id in this table... 

Consider creating a id column and increasing it by the numbers of the lines in the table, based on date or something if you don't want to get hurt in the future...