检查记录是否在Oracle中最有效的方法是什么? [英] What's the most efficient way to check if a record exists in Oracle?

问题描述

A)

select decode(count(*), 0, 'N', 'Y') rec_exists
from (select 'X'
      from dual
      where exists (select 'X'
                    from sales
                    where sales_type = 'Accessories'));

B)

select decode(count(*), 0, 'N', 'Y') rec_exists
from (select 'X'
      from sales
      where sales_type = 'Accessories'); 

C)其他(指定)

很难选择正确的"答案，因为最佳方法取决于检查值是否存在之后要执行的操作，如APC所指出的那样.我最终选择了RedFilter作为答案，因为我最初将此项检查本身设想为一个功能.

It was hard to pick the "correct" answer, as the best approach depends on what you want to do after checking if the value exists, as pointed out by APC. I ended up picking the answer by RedFilter, since I had originally envisioned this check as a function by itself.

推荐答案

select case 
            when exists (select 1 
                         from sales 
                         where sales_type = 'Accessories') 
            then 'Y' 
            else 'N' 
        end as rec_exists
from dual;

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