New-style hints: [NO_]DERIVED_CONDITION_PUSHDOWN, [NO_]MERGE

When a query filters results with a WHERE condition, that query may be more efficient when the optimizer pushes all or part of the WHERE condition down into a derived table, if a derived table is indeed present in the query. The DERIVED_CONDITION_PUSHDOWN hint explicitly tells the optimizer to apply this optimization, even if the condition_pushdown_for_derived optimizer switch is off. Conversely, NO_DERIVED_CONDITION_PUSHDOWN lets you turn it off for specific queries. Derived tables can sometimes be "merged" into the main query, essentially treating them as if they were part of the original table. This can lead to more efficient execution plans. For example, SELECT a+2 FROM (select b*2+1 as a from t1) t; will be merged such that the derived table t is removed and the selected columns recombined, resulting in SELECT b*2+3 FROM t1; The MERGE hint forces this behavior, while NO_MERGE prevents it.