Defines the interface for passing down a relational UNION operation to the DSII. More...
Public Member Functions
< DSIExtResultSet >
|Passdown (AEUnion *in_node)=0|
|Pass down the given UNION operation. |
Protected Member Functions
Defines the interface for passing down a relational UNION operation to the DSII.
A relational UNION operation combines the results of two or more queries into a single result set that include all the rows that belong to all queries in the union.
Basically, if both relational operations proceeding an UNION relational operation are successfully passed down, the UNION operation can be passed down.
Simba SQLEngine will always attempt to pass down both queries before attempting to pass down UNION. In other words, the handler to perform UNION pass-down will never be invoked if any of the queries are not passed down successfully.
Pass down the given UNION operation.
An implementation _MUST_ ensure that this method returns the table representing the union result if and only if the whole union operation is successfully passed down. Otherwise, it should return NULL and in_node remains intact.
|in_node||The union operation node. Cannot be NULL. (NOT OWN)|