为什么要使用JOIN子句而不是WHERE条件? [英] Why use a JOIN clause versus a WHERE condition?

问题描述

我针对Oracle数据库进行开发.当我需要手动编写(不使用像休眠这样的ORM)时，我使用WHERE条件而不是JOIN.

I develop against Oracle databases. When I need to manually write (not use an ORM like hibernate), I use a WHERE condition instead of a JOIN.

例如(这只是为了说明样式而简化):

for example (this is simplistic just to illustrate the style):

Select *
from customers c, invoices i, shipment_info si
where c.customer_id = i.customer_id
    and i.amount > 999.99 
    and i.invoice_id = si.invoice_id(+)  -- added to show a replacement for a join
order by i.amount, c.name

我从OLD oracle DBA学习了这种风格.从那以后，我了解到这不是标准的SQL语法.除了非标准且数据库可移植性更差以外，使用此格式还有其他影响吗?

I learned this style from an OLD oracle DBA. I have since learned that this is not standard SQL syntax. Other than being non-standard and much less database portable, are there any other repercussions to using this format?

推荐答案

有人会说这种样式可读性较差，但这是一个习惯问题.从性能的角度来看，这无关紧要，因为查询优化器会解决这个问题.

Some people will say that this style is less readable, but that's a matter of habit. From a performance point of view, it doesn't matter, since the query optimizer takes care of that.

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