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Simplify coalesce expressions #12192

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Simplify coalesce expressions #12192

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31 changes: 26 additions & 5 deletions presto-main/src/main/java/com/facebook/presto/sql/planner/ExpressionInterpreter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,7 @@
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;
Expand All @@ -122,6 +123,7 @@
import static com.facebook.presto.sql.analyzer.ExpressionAnalyzer.createConstantAnalyzer;
import static com.facebook.presto.sql.analyzer.TypeSignatureProvider.fromTypes;
import static com.facebook.presto.sql.gen.VarArgsToMapAdapterGenerator.generateVarArgsToMapAdapter;
import static com.facebook.presto.sql.planner.DeterminismEvaluator.isDeterministic;
import static com.facebook.presto.sql.planner.iterative.rule.CanonicalizeExpressionRewriter.canonicalizeExpression;
import static com.facebook.presto.type.LikeFunctions.isLikePattern;
import static com.facebook.presto.type.LikeFunctions.unescapeLiteralLikePattern;
Expand All @@ -132,6 +134,7 @@
import static com.google.common.base.Throwables.throwIfInstanceOf;
import static com.google.common.base.Verify.verify;
import static com.google.common.collect.ImmutableList.toImmutableList;
import static com.google.common.collect.Iterables.getOnlyElement;
import static java.lang.String.format;
import static java.util.Objects.requireNonNull;

Expand Down Expand Up @@ -546,19 +549,37 @@ protected Object visitCoalesceExpression(CoalesceExpression node, Object context
List<Object> values = node.getOperands().stream()
.map(value -> processWithExceptionHandling(value, context))
.filter(Objects::nonNull)
.flatMap(expression -> {
if (expression instanceof CoalesceExpression) {
return ((CoalesceExpression) expression).getOperands().stream();
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@sopel39 sopel39 Jan 8, 2019

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what if there are more levels of recursion? Make it recursive

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@Praveen2112 Praveen2112 Jan 8, 2019

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But the current model is recursive right. We have added tests with more levels of coalesce and it passed it.

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@sopel39 sopel39 Jan 8, 2019

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It only supports one level of recursion.

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@Praveen2112 Praveen2112 Jan 9, 2019

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Won't ExpressionInterpreter#processWithExceptionHandling will call other levels ? We just need to check if one of argument is of CoalesceExpression If yes we will extract its arguments and push it to the outer expression and processWithExceptionHandling will ideally handle at more levels

If I am not wrong recursive implementation will simplify
coalesce(coalesce(unbound_long, coalesce(unbound_long, 1)), unbound_long2) to coalesce(unbound_long, 1)

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@sopel39 sopel39 Jan 9, 2019

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Right, thanks

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@Praveen2112 Praveen2112 Jan 11, 2019

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Sorry I have replaced it with isDeterministic((CoalesceExpression) expression)

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@sopel39 sopel39 Jan 11, 2019

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I mean I think that isDeterministic((CoalesceExpression) expression) can be removed completely. We don't need to check if nested coalesce is deterministic

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@Praveen2112 Praveen2112 Jan 11, 2019

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But in that case it will simplify coalesce(unbound_long, coalesce(random(), 1) to coalesce(unbound_long, random(), 1).

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@Praveen2112 Praveen2112 Jan 12, 2019

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@sopel39 Removed the deterministic check as it is not required now

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@sopel39 sopel39 Jan 14, 2019

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Thank you. Ping us when release is done to land it

}
return Stream.of(expression);
})
.collect(Collectors.toList());

if ((!values.isEmpty() && !(values.get(0) instanceof Expression)) || values.size() == 1) {
return values.get(0);
}

List<Expression> expressions = values.stream()
.map(value -> toExpression(value, type))
.collect(Collectors.toList());
ImmutableList.Builder<Expression> operandsBuilder = ImmutableList.builder();
Set<Expression> visitedExpression = new HashSet<>();
for (Object value : values) {
Expression expression = toExpression(value, type);
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if (!isDeterministic(expression) || visitedExpression.add(expression)) {
operandsBuilder.add(expression);
}
if (expression instanceof Literal) {
break;
}
}
List<Expression> expressions = operandsBuilder.build();

if (expressions.isEmpty()) {
return null;
}

if (expressions.size() == 1) {
return getOnlyElement(expressions);
}
return new CoalesceExpression(expressions);
}

Expand Down Expand Up @@ -642,7 +663,7 @@ else if (!found && result) {
.filter(DeterminismEvaluator::isDeterministic)
.distinct(),
expressionValues.stream()
.filter((expression -> !DeterminismEvaluator.isDeterministic(expression))))
.filter((expression -> !isDeterministic(expression))))
.collect(toImmutableList());
return new InPredicate(toExpression(value, type), new InListExpression(simplifiedExpressionValues));
}
Expand Down
15 changes: 14 additions & 1 deletion presto-main/src/test/java/com/facebook/presto/sql/TestExpressionInterpreter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,7 @@ public class TestExpressionInterpreter
.put(new Symbol("unbound_integer"), INTEGER)
.put(new Symbol("unbound_long"), BIGINT)
.put(new Symbol("unbound_long2"), BIGINT)
.put(new Symbol("unbound_long3"), BIGINT)
.put(new Symbol("unbound_string"), VARCHAR)
.put(new Symbol("unbound_double"), DOUBLE)
.put(new Symbol("unbound_boolean"), BOOLEAN)
Expand Down Expand Up @@ -1136,7 +1137,19 @@ public void testCoalesce()
assertOptimizedEquals("coalesce(2 * 3 * unbound_integer, 1.0E0/2.0E0, null)", "coalesce(6 * unbound_integer, 0.5E0)");
assertOptimizedEquals("coalesce(unbound_integer, 2, 1.0E0/2.0E0, 12.34E0, null)", "coalesce(unbound_integer, 2.0E0, 0.5E0, 12.34E0)");
assertOptimizedMatches("coalesce(0 / 0 > 1, unbound_boolean, 0 / 0 = 0)",
"coalesce(cast(fail() as boolean), unbound_boolean, cast(fail() as boolean))");
"coalesce(cast(fail() as boolean), unbound_boolean)");
assertOptimizedMatches("coalesce(unbound_long, unbound_long)", "unbound_long");
assertOptimizedMatches("coalesce(2 * unbound_long, 2 * unbound_long)", "BIGINT '2' * unbound_long");
assertOptimizedMatches("coalesce(unbound_long, unbound_long2, unbound_long)", "coalesce(unbound_long, unbound_long2)");
assertOptimizedMatches("coalesce(unbound_long, unbound_long2, unbound_long, unbound_long3)", "coalesce(unbound_long, unbound_long2, unbound_long3)");
assertOptimizedEquals("coalesce(6, unbound_long2, unbound_long, unbound_long3)", "6");
assertOptimizedEquals("coalesce(2 * 3, unbound_long2, unbound_long, unbound_long3)", "6");
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assertOptimizedMatches("coalesce(unbound_long, coalesce(unbound_long, 1))", "coalesce(unbound_long, BIGINT '1')");
assertOptimizedMatches("coalesce(coalesce(unbound_long, coalesce(unbound_long, 1)), unbound_long2)", "coalesce(unbound_long, BIGINT '1')");
assertOptimizedMatches("coalesce(unbound_long, 2, coalesce(unbound_long, 1))", "coalesce(unbound_long, BIGINT '2')");
assertOptimizedMatches("coalesce(coalesce(unbound_long, coalesce(unbound_long2, unbound_long3)), 1)", "coalesce(unbound_long, unbound_long2, unbound_long3, BIGINT '1')");
assertOptimizedMatches("coalesce(unbound_double, coalesce(random(), unbound_double))", "coalesce(unbound_double, random())");
assertOptimizedMatches("coalesce(random(), random(), 5)", "coalesce(random(), random(), 5E0)");
}

@Test
Expand Down