SQL JOIN 和 INNER JOIN 的区别
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Difference between JOIN and INNER JOIN
提问by driis
Both these joins will give me the same results:
这两个连接都会给我相同的结果：
SELECT * FROM table JOIN otherTable ON table.ID = otherTable.FK
vs
对比
SELECT * FROM table INNER JOIN otherTable ON table.ID = otherTable.FK
Is there any difference between the statements in performance or otherwise?
性能或其他方面的陈述之间有什么区别吗？
Does it differ between different SQLimplementations?
不同的SQL实现之间有区别吗？
回答by palehorse
They are functionally equivalent, but INNER JOINcan be a bit clearer to read, especially if the query has other join types (i.e. LEFTor RIGHTor CROSS) included in it.
它们在功能上是等效的，但INNER JOIN读起来会更清晰一些，尤其是当查询中包含其他连接类型（即LEFTorRIGHT或CROSS）时。
回答by Quassnoi
No, there is no difference, pure syntactic sugar.
不，没有区别，纯语法糖。
回答by net_prog
INNER JOIN = JOIN
内连接 = 连接
INNER JOIN is the default if you don't specifythe type when you use the word JOIN.
You can also use LEFT OUTER JOIN or RIGHT OUTER JOIN, in which case the word OUTER is optional, or you can specify CROSS JOIN.
如果您在使用 JOIN 一词时未指定类型，则INNER JOIN 是默认值。
您还可以使用 LEFT OUTER JOIN 或 RIGHT OUTER JOIN，在这种情况下，OUTER 一词是可选的，或者您可以指定 CROSS JOIN。
OR
或者
For an inner join, the syntax is:
SELECT ...
FROM TableA
[INNER] JOIN TableB(in other words, the "INNER" keyword is optional- results are the same with or without it)
对于内部联接，语法为：
SELECT ...
FROM TableA
[INNER] JOIN TableB（换句话说，“INNER”关键字是可选的- 无论有没有它，结果都是一样的）
回答by Micha? Powaga
Does it differ between different SQL implementations?
不同的 SQL 实现之间有区别吗？
Yes, Microsoft Accessdoesn't allow just join. It requires inner join.
是的，Microsoft Access不允许仅join. 它需要inner join.
回答by Kristen
Similarly with OUTER JOINs, the word "OUTER"is optional. It's the LEFTor RIGHTkeyword that makes the JOINan "OUTER" JOIN.
与 类似OUTER JOINs，这个词"OUTER"是可选的。是LEFTorRIGHT关键字使JOINan "OUTER" JOIN。
However for some reason I always use "OUTER"as in LEFT OUTER JOINand never LEFT JOIN, but I never use INNER JOIN, but rather I just use "JOIN":
但是出于某种原因，我总是使用"OUTER"as inLEFT OUTER JOIN并且从不使用LEFT JOIN，但我从不使用INNER JOIN，而是我只是使用"JOIN"：
SELECT ColA, ColB, ...
FROM MyTable AS T1
JOIN MyOtherTable AS T2
ON T2.ID = T1.ID
LEFT OUTER JOIN MyOptionalTable AS T3
ON T3.ID = T1.ID
回答by Martin Smith
As the other answers already state there is no difference in your example.
正如其他答案已经指出的那样，您的示例没有区别。
The relevant bit of grammar is documented here
相关的语法部分记录在此处
<join_type> ::=
[ { INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } } [ <join_hint> ] ]
JOIN
Showing that all are optional. The page further clarifies that
显示所有都是可选的。该页面进一步阐明
INNERSpecifies all matching pairs of rows are returned. Discards unmatched rows from both tables. When no join type is specified, this is the default.
INNER指定返回所有匹配的行对。丢弃两个表中不匹配的行。当未指定联接类型时，这是默认值。
The grammar does also indicate that there is one time where the INNERisrequired though. When specifying a join hint.
语法确实也表明，有其中一次INNER是必需的，但。指定连接提示时。
See the example below
看下面的例子
CREATE TABLE T1(X INT);
CREATE TABLE T2(Y INT);
SELECT *
FROM T1
LOOP JOIN T2
ON X = Y;
SELECT *
FROM T1
INNER LOOP JOIN T2
ON X = Y;
