INNER JOIN and JOIN have the same function just to make it clearer to read, you can specify INNER JOIN. If the query has another join type such as LEFT, RIGHT or CROSS then include it.
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Refer to this video about INNER JOIN in detail.
You can also say that JOIN = INNER JOIN
The syntax for INNER JOIN is:
SELECT C1, C2, C3
[INNER] JOIN TABLE2
Note: INNER Keyword is optional here. Even though you don’t mention it. By default, the INNER JOIN will be applicable.