'LEFT JOIN' vs 'LEFT OUTER JOIN'

问题

I know there is really no difference, but is 'LEFT JOIN' an ANSI form or are there any RDBMS's that will fail 'LEFT JOIN' and require 'LEFT OUTER JOIN'. [I am asking here so I can save a few clicks, form fillings, etc to get the correct ANSI standard!]

回答1:

[OUTER] is optional, per the ANSI spec (92, but I'm sure later versions also cover it).

Of course, you're assuming that every SQL product is ANSI compatible. For joins, they probably are..

回答2:

ANSI JOINS

http://www.oratechinfo.co.uk/ansi_joins.html

Note, the OUTER can be dropped, since, by definition, LEFT, RIGHT and FULL JOINs MUST be OUTER joins (it's down to personal preference and readability)

来源：https://stackoverflow.com/questions/6625964/left-join-vs-left-outer-join