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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]# Derive Additional Filters

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In org.apache.calcite.rel.rules.FilterJoinRule, there's the following comment // TODO - add logic to derive additional filters. E.g., from // (t1.a = 1 AND t2.a = 2) OR (t1.b = 3 AND t2.b = 4), you can // derive table filters: // (t1.a = 1 OR t1.b = 3) // (t2.a = 2 OR t2.b = 4) When perf-testing TPC-H/DS queries, we found that such additional filters would have been very profitable in several cases. Has anybody worked on this issue or is there already a util to that effect? The following algorithm is what I am thinking; please comment if interested. Given a predicate p, we want to derive an implied predicate q, i.e. p->q, and q only references columns on a specified side of a join. Then we can transform p to AND(p, q); q will be pushed down at a later stage. Since we are dealing with 3-value booleans, we need to be very careful. To be precise, we need a function T(p) which returns a predicate such that for any row, if p evaluates to TRUE, T(p) must also evaluate to TRUE. To handle NOT, we also need a function F(p) such that for any row, if p evaluates to FALSE, F(p) must also evaluate to FALSE. T(p) can be defined as such -- T( p ) => p, if p only references a specified side of a join T( OR(a,b) ) => OR(T(a), T(b)) T( AND(a,b) ) => AND(T(a), T(b)) T( NOT(p) ) => NOT( F(p) ) T( p ) => TRUE, for all other cases, as the fallback // not a present concern, but more rules can be plugged into T(p) if // desired in some applications, e.g. T( x*x+y*y<100 ) => x*x<100 F(p) is defined similarly -- F( p ) => p, if p only references a specified side of a join F( OR(a,b) ) => OR(F(a), F(b)) F( AND(a,b) ) => AND(F(a), F(b)) F( NOT(p) ) => NOT( T(p) ) F( p ) => FALSE, for all other cases, as the fallback We can unify T(p) and F(p) as one function X(v,p), where v is TRUE/FALSE. For any row, if p evaluates to v, then X(v,p) also evaluates to v. (The case of UNKNOWN seems very difficult, I'm not considering it here.)

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