replacing TSQL NOT EXISTS in SQL-92

Question

I am have following code which works well in TSQL:

BEGIN 
IF NOT EXISTS (select * from tblDCUSTOM where id = 'All Customers')
    BEGIN
    INSERT INTO tblDCUSTOM
        (ID
    ,Name
    ,English     
   )
   SELECT 'All Customers','All Customers','All Customers'
   END
END

Now, I need to have this functionality in an custom environment, where SQL-92 is used - so no EXISTS (edit: not true, EXISTS works in SQL-92) or BEGIN-END is possible. Any Ideas?

Answer 1

As per very first comment;

   INSERT INTO tblDCUSTOM
        (ID
    ,Name
    ,English     
   )
   SELECT 'All Customers','All Customers','All Customers'
   WHERE (SELECT COUNT(*) FROM tblDCUSTOM where id = 'All Customers') >= 1

If TOP is supported this might be better

   INSERT INTO tblDCUSTOM
        (ID
    ,Name
    ,English     
   )
   SELECT 'All Customers','All Customers','All Customers'
   WHERE (SELECT TOP 1 1 as F FROM tblDCUSTOM where id = 'All Customers') IS NOT NULL

I must warn you, many have tried to make a 'database agnostic' system. It's not worth it.