Partial passthrough of the statement

If a statement contains references to multiple servers, or uses SQL features not supported by a remote server, the query is decomposed into simpler parts.

SELECT statements are broken down by removing portions that cannot be passed on and letting Sybase IQ perform the feature. For example, assume that a remote server cannot process the atan2() function in the following statement:

select acol, bcol, ccol
where atan2(bcol,10) > 3
and ccol = 10

The statement sent to the remote server is converted to:

select acol, bcol, ccol
where ccol = 10 

Locally, Sybase IQ applies “where atan2(bcol,10) > 3" to the intermediate result set.

Sybase IQ processes joins involving remote tables using a nested loop algorithm. When two tables are joined, one table is selected to be the outer table. The outer table is scanned based on the WHERE conditions that apply to it. For every qualifying row found, the other table, known as the inner table is scanned to find a row that matches the join condition.

Since the cost of searching a remote table is usually much higher than a local table (due to network I/O), every effort is made to make the remote table the outermost table in the join.

You can issue an UPDATE or DELETE on a proxy table for a remote server that supports updates, as long as the query can be passed off completely.

For example, you can send the following update to a remote Sybase IQ 12.4.3 or higher database:

UPDATE t1 
SET a = atan2(b, 10)
WHERE b > 5

If Sybase IQ cannot pass off an UPDATE or DELETE completely, or if you send the query to a remote server that does not support updates, you receive an error. Sybase IQ does not support positioned updates on remote data.