This SHOWPLAN step indicates an existence test that is generated by the optimizer when modifying a view that involves one or more subqueries and was created WITH CHECK OPTION. If the existence test fails, the modification will also fail.
Assuming the following view:
CREATE VIEW v1 AS SELECT * FROM mytable WHERE col1 IN (SELECT col1 FROM mytable2) WITH CHECK OPTION
the following example demonstrates the SHOWPLAN output for a query which updates a view containing subqueries which was created WITH CHECK OPTION.
UPDATE v1 SET col1 = 2
STEP 1 The type of query is UPDATE The update mode is deferred FROM TABLE mytable Nested iteration Table Scan FROM TABLE mytable2 EXISTS TABLE : nested iteration Table Scan TO TABLE mytable WITH CHECK OPTION FROM TABLE mytable2 EXISTS TABLE : nested iteration Table Scan