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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?



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

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