See https://github.com/teiid/teiid/blob/d0f6217824b0c4d64b1d166e8f7c69529acdface/engine/src/test/java/org/teiid/query/processor/TestTriggerActions.java#L277 Given that IS DISTINCT prior to 10.0 is restricted to IF statements in procedures, this needs to should be tested using an update trigger. See the test case, both the new and the old row value contain a column with a value of null - as the GX view is defined with the second branch as "select null as x" and the user update "update gx set x = x || 'a' where y = 2" expression for the x value evaluates to null for that row.