morrySnow commented on code in PR #51928:
URL: https://github.com/apache/doris/pull/51928#discussion_r2158920315
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fe/fe-core/src/main/java/org/apache/doris/nereids/rules/analysis/SubqueryToApply.java:
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@@ -404,7 +404,13 @@ private Pair<LogicalPlan, Optional<Expression>>
addApply(SubqueryExpr subquery,
// we use needRuntimeAnyValue to indicate if any_value() is needed
// if needRuntimeAnyValue is true, we will add it to the project list
boolean needRuntimeAnyValue = false;
- NamedExpression oldSubqueryOutput =
subquery.getQueryPlan().getOutput().get(0);
+ // For the unCorrelate case:
+ // 1. `t1.a = (select t2.x from t2 limit 1)`, subquery output t2.x
maybe null if subquery output 0 rows;
+ // 2. `t1.a = (select count(t2.x) from t2)`, subquery output
count（t2.x) is always not nullable;
+ // When given a slot reference S, we don't know S is t2.x or
count(t2.x),
+ // For safety reason, we treat S as nullable. even S is count(t2.x),
+ // we may have performance downgrade, but the execute result still be
right.
+ NamedExpression oldSubqueryOutput =
subquery.getQueryPlan().getOutput().get(0).withNullable(true);
Review Comment:
could we use `subquery.getSubqueryOutput()` here
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