Thom Brown wrote:
SELECT tbl_a.location, tbl_b.language
FROM tbl_c
NATURAL INNER JOIN tbl_a
NATURAL INNER JOIN tbl_b
The confusion comes when 2 of those tables reference the 3rd table using
the same column.
So are natural joins only allowed to join 2 tables? If not, how can it
be used for more than 1 table has links to the other tables?
The fact that the above example runs proves that natural joins are
allowed with more than 2 tables.
Joins nest from left to write, so
tbl_c NATURAL JOIN tbl_a NATURAL JOIN tbl_b
means
(tbl_c NATURAL JOIN tbl_a) NATURAL JOIN tbl_b
and that means that the second join is executed as if the first join
resulted in a normal table with normal columns with names as the case
may be, and the natural join will use those names with all the consequences.
If you want a different order, you can set the parentheses differently,
with possibly different results.
The fact that this isn't entirely obvious only supports the argument
that natural joins shouldn't used.
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