5.8 Methods for processing set operations
If you specify a set operation (excluding UNION ALL), the set operation is executed by using either of the following processing methods:
-
Hash execution
-
Work table execution
HADB automatically determines which method to use. You can find out which processing method is used by viewing the access path. For details about access paths, see the following sections:
-
How to check access paths
-
Information that is displayed as access paths
See (12) Processing method for duplicate removal in 6.1.4 Information displayed in the tree view.
- Note
-
-
You can prevent the application of hash execution by specifying a set operation method specification. For details about set operation method specifications, see Specification format and rules for query expressions in the manual HADB SQL Reference.
-
If you specify UNION ALL, data of the query expression body specified in the operands of the set operation will be returned as is.
-
- Organization of this section