On 07/28/2012 03:36 PM, Dan wrote:
An example of an inner join:
"table1" INNER JOIN "table2" ON "table1"."foreign
key"="table2"."primary key"
Mathematically the following seems to be possible:
"table1" INNER JOIN "table2" ON "table1"."foreign
key"=2*"table2"."primary key"
Is the latter also an INNER JOIN? There seems to be other possible
multipliers other than 2. Also, what about inequalities? For example,
wanting to see all the rows of data for which the foreign key is less
than the MAX, MIN, or Ave of the primary key. (These are three
suggested "ON expressions" for an INNER JOIN. Using greater than
rather than less than is another possibility.)
I'm curious since I have a mathematical background. Any ideas?
--Dan
Dan
If understand the keys they are not required to be integers though they
usually are. The major requirement for a key is that it is unique and
only exist once in the table. Keys can include multiple columns. So
multiplying a key would often not make sense. I believe you can add more
requirements in the ON clause.
The reason keys are often integers is that one often defines the key as
integer with automatic incrementing when a new row is added.
--
Jay Lozier
[email protected]
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