morrySnow commented on code in PR #27471:
URL: https://github.com/apache/doris/pull/27471#discussion_r1405645714
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/Expression.java:
##########
@@ -223,6 +224,10 @@ public Expression withChildren(List<Expression> children) {
* Whether the expression is a constant.
*/
public boolean isConstant() {
+ if (this instanceof AggregateFunction) {
Review Comment:
do we need add window expression and tvf?
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/CountLiteralRewrite.java:
##########
@@ -21,31 +21,59 @@
import org.apache.doris.nereids.rules.RuleType;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.NamedExpression;
+import org.apache.doris.nereids.trees.expressions.StatementScopeIdGenerator;
import
org.apache.doris.nereids.trees.expressions.functions.agg.AggregateFunction;
import org.apache.doris.nereids.trees.expressions.functions.agg.Count;
+import org.apache.doris.nereids.trees.expressions.literal.BigIntLiteral;
+import org.apache.doris.nereids.trees.plans.Plan;
+import org.apache.doris.nereids.trees.plans.logical.LogicalOneRowRelation;
+import org.apache.doris.nereids.trees.plans.logical.LogicalProject;
import com.google.common.collect.Lists;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
+import java.util.stream.Collectors;
/**
* count(1) ==> count(*)
+ * count(null) ==> 0
*/
-public class CountLiteralToCountStar extends OneRewriteRuleFactory {
+public class CountLiteralRewrite extends OneRewriteRuleFactory {
@Override
public Rule build() {
return logicalAggregate().then(
agg -> {
List<NamedExpression> newExprs =
Lists.newArrayListWithCapacity(agg.getOutputExpressions().size());
- if (rewriteCountLiteral(agg.getOutputExpressions(),
newExprs)) {
- return agg.withAggOutput(newExprs);
+ if (!rewriteCountLiteral(agg.getOutputExpressions(),
newExprs)) {
+ // no need to rewrite
+ return agg;
+ }
+
+ Map<Boolean, List<NamedExpression>> projectsAndAggFunc =
newExprs.stream()
+
.collect(Collectors.partitioningBy(Expression::isConstant));
+
+ if (projectsAndAggFunc.get(false).isEmpty()) {
+ // if there is no group by keys and other agg func,
just return the one row Relations, such as
+ // select count(null) from t
Review Comment:
it is not right when base table is empty, think about
```sql
select 'abc' from t group by 'abc'
```
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