Defines the interface for passing down a relational DISTINCT operation to the DSII. More...
Public Member Functions
< DSIExtResultSet >
|Passdown (AEDistinct *in_node)=0|
|Pass down the DISTINCT operation. |
Protected Member Functions
Defines the interface for passing down a relational DISTINCT operation to the DSII.
A relational DISTINCT operation is used to remove duplicates from the result set of a select statement. When there is only one column provided in the table on which DISTINCT is operated, the result will be the unique values of that column. When there are multiple columns provided in the table, the result will be the unique combinations of the columns.
Simba SQLEngine will attempt to pass down the DISTINCT operation to the DSII. If the DSII is able to operate DISTINCT, the table with unique rows representing the result set of DISTINCT will be returned to the engine. Otherwise, NULL will be returned and the engine will do the DISTINCT operation.
Pass down the DISTINCT operation.
An implementation should ensure that this method returns the table representing the distinct result if the distinct operation is successfully passed down. Otherwise, it should return NULL and in_node remains intact.
|in_node||The distinct operation node. Cannot be NULL. (NOT OWN)|