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From comnetwork <>
Subject [GitHub] phoenix pull request #417: PHOENIX-4820
Date Sat, 22 Dec 2018 02:40:58 GMT
Github user comnetwork commented on a diff in the pull request:
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/expression/ ---
    @@ -88,4 +88,10 @@
          * @return
         boolean requiresFinalEvaluation();
    --- End diff --
    ExpressionUtil.isConstant(Expression) is not suitable for OrderPreservingTracker.IsConstantVisitor,
because ExpressionUtil.isConstant(Expression) depends on Expression.isStateless() and Expression.getDeterminism().
Expression isStateless() is to check if the expression is depend on the server state, even
for RowKeyColumnExpression , isStateless() is false. What we want to check is if a expression
is constant when all children of it are constants, just consider following sql:
    select a.ak3 from
    (select rand() ak1,length(pk2) ak2,length(pk3) ak3,length(v1) av1,length(v2) av2 from
test order by pk2,pk3 limit 10) a
    where a.ak1 = 0.0 and a.av2 = length(substr('abc',1,1))
    group by a.ak3,CASE WHEN coalesce(a.ak1,1) > coalesce(a.av2,2) THEN coalesce(a.ak1,1)
ELSE coalesce(a.av2,2) END,a.av1
    order by a.ak3,a.av1
    Obviously , because of rand(), the Determinism of expression a.ak1 is Determinism.PER_INVOCATION,
so for expression "CASE WHEN coalesce(a.ak1,1) > coalesce(a.av2,2) THEN coalesce(a.ak1,1)
ELSE coalesce(a.av2,2) END", the determinism is Determinism.PER_INVOCATION and isStateless
is false , but because the a.ak1 and a.av2 are both constants in where clause of outer query,
we can regard "CASE WHEN coalesce(a.ak1,1) > coalesce(a.av2,2) THEN coalesce(a.ak1,1) ELSE
coalesce(a.av2,2) END" as constant in IsConstantVisitor.
    BTW. The value returned by ExpressionUtil.isConstant() is complicated and runtime related
because of Expression.getDeterminism(). In following BaseCompoundExpression.init method, determinism
is the combine of its children.
    ` private void init(List<Expression> children) {
            this.children = ImmutableList.copyOf(children);
            boolean isStateless = true;
            boolean isNullable = false;
            boolean requiresFinalEvaluation = false;
            this.determinism = Determinism.ALWAYS;
            for (int i = 0; i < children.size(); i++) {
                Expression child = children.get(i);
                isNullable |= child.isNullable();
                isStateless &= child.isStateless();
                this.determinism = this.determinism.combine(child.getDeterminism());
                requiresFinalEvaluation |= child.requiresFinalEvaluation();
            this.isStateless = isStateless;
            this.isNullable = isNullable;
            this.requiresFinalEvaluation = requiresFinalEvaluation;


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