mysql SELECT"FROM t1，t2"； -或者-"FROM t1 JOIN t2 ON"； [英] mysql SELECT "FROM t1, t2" -or- "FROM t1 JOIN t2 ON"

问题描述

此查询之间有什么区别?我应该选择哪一个?为什么?

what is the different between this queries? which one should I prefer and why?

SELECT
t1.*,
t2.x
FROM
t1,
t2
WHERE
t2.`id` = t1.`id`

或

SELECT
t1.*,
t2.x
FROM
t1
INNER JOIN                                                  # LEFT JOIN ?
t2
ON t2.`id` = t1.`id`

使用逗号与使用LEFT JOINS具有相同的效果吗?

Does using commas has the same effect than use LEFT JOINS?

这很尴尬.多年来，这是我第一次问自己.我曾经使用过第一个版本，但是现在感觉就像我在第一个SQL归纳中错过了几行. ;)

That's embarrassing. It's the first time I asked myself about this for years. I ever used the first version, but now i'm feeling like I missed some lines in my first SQL induction. ;)

推荐答案

逗号"语法等效于INNER JOIN语法.无论您如何查询，查询优化器都应该为您运行相同的查询.一般建议使用JOIN语言进行联接，并使用WHERE语言进行过滤，因为这样可以使您的意图更加明确

The "comma" syntax is equivalent to the INNER JOIN syntax. The query optimizer should be running the same query for you regardless of how you ask for it. There's a general recommendation to do your joins using the JOIN language and do your filtering using the WHERE language as it makes your intention more clear

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