为什么使用 JOIN 子句而不是 WHERE 条件?

Why use a JOIN clause versus a WHERE condition?(为什么使用 JOIN 子句而不是 WHERE 条件?)

问题描述

我针对 Oracle 数据库进行开发.当我需要手动编写(而不是使用像 hibernate 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单化):

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

我从一位老 Oracle DBA 那里学到了这种风格.我后来了解到这不是标准的 SQL 语法.除了非标准和数据库可移植性低得多之外，使用这种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

有些人会说这种风格可读性较差，但这是习惯问题.从性能的角度来看，这并不重要，因为查询优化器会负责.

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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