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[fix](nereids)count in correlated subquery shoud not output null value #27064

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Nov 17, 2023
Merged

[fix](nereids)count in correlated subquery shoud not output null value #27064

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19 changes: 18 additions & 1 deletion fe/fe-core/src/main/java/org/apache/doris/nereids/rules/expression/rules/FunctionBinder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -49,8 +49,11 @@
import org.apache.doris.nereids.trees.expressions.WhenClause;
import org.apache.doris.nereids.trees.expressions.functions.BoundFunction;
import org.apache.doris.nereids.trees.expressions.functions.FunctionBuilder;
import org.apache.doris.nereids.trees.expressions.functions.agg.Count;
import org.apache.doris.nereids.trees.expressions.functions.scalar.Lambda;
import org.apache.doris.nereids.trees.expressions.functions.scalar.Nvl;
import org.apache.doris.nereids.trees.expressions.functions.udf.AliasUdfBuilder;
import org.apache.doris.nereids.trees.expressions.literal.BigIntLiteral;
import org.apache.doris.nereids.trees.expressions.typecoercion.ImplicitCastInputTypes;
import org.apache.doris.nereids.types.ArrayType;
import org.apache.doris.nereids.types.BigIntType;
Expand Down Expand Up @@ -167,7 +170,21 @@ public Expression visitUnboundFunction(UnboundFunction unboundFunction, Expressi
// we do type coercion in build function in alias function, so it's ok to return directly.
return builder.build(functionName, arguments);
} else {
return TypeCoercionUtils.processBoundFunction((BoundFunction) builder.build(functionName, arguments));
Expression boundFunction = TypeCoercionUtils
.processBoundFunction((BoundFunction) builder.build(functionName, arguments));
if (boundFunction instanceof Count
&& context.cascadesContext.getOuterScope().isPresent()
&& !context.cascadesContext.getOuterScope().get().getCorrelatedSlots()
.isEmpty()) {
// consider sql: SELECT * FROM t1 WHERE t1.a <= (SELECT COUNT(t2.a) FROM t2 WHERE (t1.b = t2.b));
// when unnest correlated subquery, we create a left join node.
// outer query is left table and subquery is right one
// if there is no match, the row from right table is filled with nulls
// but COUNT function is always not nullable.
// so wrap COUNT with Nvl to ensure it's result is 0 instead of null to get the correct result
boundFunction = new Nvl(boundFunction, new BigIntLiteral(0));
}
return boundFunction;
}
}

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5 changes: 5 additions & 0 deletions regression-test/suites/nereids_p0/subquery/test_subquery.groovy
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Expand Up @@ -118,6 +118,11 @@ suite("test_subquery") {
contains("VAGGREGATE")
}

explain {
sql """SELECT * FROM table_1000_undef_undef t1 WHERE t1.pk <= (SELECT COUNT(t2.pk) FROM table_1000_undef_undef2 t2 WHERE (t1.col_bigint_undef_signed = t2.col_bigint_undef_signed)); """
contains("ifnull")
}

sql """DROP TABLE IF EXISTS table_1000_undef_undef"""
sql """DROP TABLE IF EXISTS table_1000_undef_undef2"""

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