如果数据记录不存在，则将其存储到另一个表中

Question

I am looking for a SQL code that is doing the following thing:

1. SELECT * FROM fzs_contest WHERE answer = 'D' order by rand() limit 1;
2. Store the result of the code above to the table fzs_contest_winners (create the table if it does not exist)
3. If the data record already exists in the table fzs_contest_winners , reapeat line #1 until it is unique.

Is that possible with SQL only?

Answer 1

How about just getting a valid winner the first time?

insert into fzs_contest_winners ( . . .)
    select . . . 
    from fzs_contest c
    where answer = 'D' and
          not exists (select 1 from fzs_context_winners cw where cw.?? = c.??)
    order by rand()
    limit 1;

The ?? is for the column that identifies someone as being the same in the two tables.

Note: This type of query could choose the same winner twice, if two threads were running at the same time. However, it seems unlikely to me that you are selecting more than one winner at a time. In addition, you should guarantee that a person only appears once in the table by using a unique index.