Adaptive Server generates an abstract plan based on the SQL syntax itself. If a SQL statement is transformed to another syntax that the Adaptive Server optimizer cannot transform internally, then the abstract plans are not compatible. Therefore, even though two SQL statements may be semantically equivalent, their abstract plans are not compatible.
For example, take this SQL statement as your original SQL statement:
SELECT A CITY FROM A, B, C
WHERE A.CITY =B.CITY
AND B.CITY=C.CITY
And take this semantically equivalent alternative SQL:
SELECT A.CITY FROM A, B, C
WHERE A.CITY =B.CITY
AND B.CITY=C.CITY
AND A.CITY=C.CITY
The transforms adds the new condition, A.CITY=C.CITY, and if the Adaptive Server optimizer cannot generate A.CITY=C.CITY internally for your original SQL, then an index scan from A.CITY to C.CITY or from C.CITY to A.CITY is not possible for your original SQL. So, the new abstract plan is not compatible for the original SQL.
Also, if an OR condition is transformed to a UNION, the new abstract plan is so different from the original SQL that there is no way for the original SQL to be compatible with the new abstract plan.
Open the Abstract Plan Manager
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