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In the Query Rewrite phase, SQL Anywhere performs a number of transformations in search of more efficient and convenient representations of the query. Because the query may be rewritten into a semantically equivalent query, the plan may look quite different from a literal interpretation of your original query. Common manipulations include:
Elimination of unnecessary DISTINCT conditions
unnesting subqueries
predicate pushdown in UNION or GROUPed views and derived tables
optimization of OR and IN-list predicates
optimization of LIKE predicates
conversion of outer joins to inner joins
elimination of outer joins and inner joins
discovery of exploitable conditions through predicate inference
elimination of unnecessary case translation
rewriting subqueries as EXISTS predicates
Elimination of unnecessary DISTINCT conditions
Unnesting subqueries
Predicate pushdown in UNION or GROUPed views and derived tables
Optimization of OR and IN-list predicates
Optimization of LIKE predicates
Conversion of outer joins to inner joins
Elimination of unnecessary inner and outer joins
Discovery of exploitable conditions through predicate inference
Elimination of unnecessary case translation
Rewriting subqueries as EXISTS predicates