slinkydeveloper commented on a change in pull request #17256:
URL: https://github.com/apache/flink/pull/17256#discussion_r707995221
##########
File path:
flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/api/Expressions.java
##########
@@ -535,6 +535,18 @@ public static ApiExpression ifThenElse(Object condition,
Object ifTrue, Object i
return apiCall(BuiltInFunctionDefinitions.IF, condition, ifTrue,
ifFalse);
}
+ /**
+ * Coalesce specifies a series of expressions, and returns the first
expression whose value is
+ * not null. If all the expressions evaluate as null, coalesce returns a
null value.
+ *
+ * <p>e.g. coalesce($("f0"), "-") leads to "-" if f0 is null
Review comment:
> Having a couple examples would be good, especially ones that don't
rely on external fields (like f0) but would work out of the box.
I think it's still worth showing with external fields, because showing the
coalesce with constants doesn't really show the point IMO. Look at the rephrase
now, i have added two examples to make my point (hopefully) clear enough.
##########
File path:
flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/inference/strategies/CoalesceTypeStrategy.java
##########
@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.types.inference.strategies;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.table.types.DataType;
+import org.apache.flink.table.types.inference.CallContext;
+import org.apache.flink.table.types.inference.TypeStrategy;
+import org.apache.flink.table.types.logical.LogicalType;
+import org.apache.flink.table.types.logical.utils.LogicalTypeMerging;
+import org.apache.flink.table.types.utils.TypeConversions;
+
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+/**
+ * A type strategy for COALESCE return type. The return type of COALESCE is
the least restrictive
+ * type of its arguments, and it's nullable only if all its input args are
nullable.
+ */
+@Internal
+public final class CoalesceTypeStrategy implements TypeStrategy {
+
+ public CoalesceTypeStrategy() {}
+
+ @Override
+ public Optional<DataType> inferType(CallContext callContext) {
Review comment:
I've reused `NullableIfArgsTypeStrategy`, removing the code here. Now
`TypeStrategies` has both `nullableIfArgs` and `nullableIfAllArgs`. Perhaps
should i rename `nullableIfArgs` in `nullableIfAnyArgs`? Should I do it in this
PR (separate commit) or another one?
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