The following table shows some of the common set operations you may encounter while using the Explain SQL window.
| Operation | Description |
|---|---|
|
CONCATENATION |
Multiple result sets are merged in the same way as in an explicit UNION statement. This typically occurs when an OR statement is used with indexed columns. |
|
INTERSECTION |
Two result sets are compared, and only rows common to both are returned. This operation usually only takes place as a result of an explicit use of the INTERSECTION clause. |
|
MINUS |
All result sets in the first result set are returned, except those appearing in the second result set. This occurs as a result of the MINUS set operator. |
|
UNION-ALL |
Two result sets are combined and rows from both returned. |
|
UNION |
Two result sets are combined and rows from both are returned. Duplicate rows are not returned. |
|
VIEW |
Either a view definition has accessed, or a temporary table has been created to store a result set. |
