Re: Searching and Cross Referencing Multiple Tables

[Rick James]

My bad -- email is in table1.

... FROM (SELECT...)

Means to create a temporary table with that inner SELECT, then use that as the "table" from which to do the outer stuff.

FROM (SELECT ...) AS a
JOIN (SELECT ...) AS b
ON a.id = b.id

creates two tmp tables, then uses them (with "aliases" a and b) in a JOIN. This example is probably terribly inefficient since neither tmp table has an index on id.

These mean virtually the same thing:
FROM t1, t2 WHERE t1.id=t2.id
FROM t1 JOIN t2 ON t1.id=t2.id